/* * Copyright (c) 2019, Alliance for Open Media. All rights reserved. * * This source code is subject to the terms of the BSD 2 Clause License and * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License * was not distributed with this source code in the LICENSE file, you can * obtain it at www.aomedia.org/license/software. If the Alliance for Open * Media Patent License 1.0 was not distributed with this source code in the * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
*/
// This is an example demonstrating how to implement a multi-layer AOM // encoding scheme for RTC video applications.
typedefstruct { constchar *output_filename; char options[OPTION_BUFFER_SIZE]; struct AvxInputContext input_ctx[MAX_NUM_SPATIAL_LAYERS]; int speed; int aq_mode; int layering_mode; int output_obu; int decode; int tune_content; int show_psnr; bool use_external_rc; bool scale_factors_explicitly_set; constchar *multilayer_metadata_file;
} AppInput;
void usage_exit(void) {
fprintf(stderr, "Usage: %s input_filename [input_filename ...] -o " "output_filename\n",
exec_name);
fprintf(stderr, "Options:\n");
arg_show_usage(stderr, svc_args);
fprintf(
stderr, "Input files must be y4m or yuv.\n" "If multiple input files are specified, they correspond to spatial " "layers, and there should be as many as there are spatial layers.\n" "All input files must have the same width, height, frame rate and number " "of frames.\n" "If only one file is specified, it is used for all spatial layers.\n"); exit(EXIT_FAILURE);
}
staticvoid open_input_file(struct AvxInputContext *input,
aom_chroma_sample_position_t csp) { /* Parse certain options from the input file, if possible */
input->file = strcmp(input->filename, "-") ? fopen(input->filename, "rb")
: set_binary_mode(stdin);
if (!input->file) fatal("Failed to open input file");
if (!fseeko(input->file, 0, SEEK_END)) { /* Input file is seekable. Figure out how long it is, so we can get * progress info.
*/
input->length = ftello(input->file);
rewind(input->file);
}
/* For RAW input sources, these bytes will applied on the first frame * in read_frame().
*/
input->detect.buf_read = fread(input->detect.buf, 1, 4, input->file);
input->detect.position = 0;
// Total bitrate needs to be parsed after the number of layers. for (argi = argj = argv; (*argj = *argi); argi += arg.argv_step) {
arg.argv_step = 1; if (arg_match(&arg, &bitrates_arg, argi)) {
aom_codec_err_t res = parse_layer_options_from_string(
svc_params, BITRATE, arg.val, svc_params->layer_target_bitrate, NULL); if (res != AOM_CODEC_OK) {
die("Failed to parse bitrates: %s\n", aom_codec_err_to_string(res));
}
} else {
++argj;
}
}
// There will be a space in front of the string options if (strlen(string_options) > 0)
strncpy(app_input->options, string_options, OPTION_BUFFER_SIZE);
// Check for unrecognized options for (argi = argv; *argi; ++argi) if (argi[0][0] == '-' && strlen(argi[0]) > 1)
die("Error: Unrecognized option %s\n", *argi);
if (argv[0] == NULL) {
usage_exit();
}
int input_count = 0; while (argv[input_count] != NULL && input_count < MAX_NUM_SPATIAL_LAYERS) {
app_input->input_ctx[input_count].filename = argv[input_count];
++input_count;
} if (input_count > 1 && input_count != svc_params->number_spatial_layers) {
die("Error: Number of input files does not match number of spatial layers");
} if (argv[input_count] != NULL) {
die("Error: Too many input files specified, there should be at most %d",
MAX_NUM_SPATIAL_LAYERS);
}
free(argv);
for (int i = 0; i < input_count; ++i) {
open_input_file(&app_input->input_ctx[i], AOM_CSP_UNKNOWN); if (app_input->input_ctx[i].file_type == FILE_TYPE_Y4M) { if (enc_cfg->g_w == 0 || enc_cfg->g_h == 0) { // Override these settings with the info from Y4M file.
enc_cfg->g_w = app_input->input_ctx[i].width;
enc_cfg->g_h = app_input->input_ctx[i].height; // g_timebase is the reciprocal of frame rate.
enc_cfg->g_timebase.num = app_input->input_ctx[i].framerate.denominator;
enc_cfg->g_timebase.den = app_input->input_ctx[i].framerate.numerator;
} elseif (enc_cfg->g_w != app_input->input_ctx[i].width ||
enc_cfg->g_h != app_input->input_ctx[i].height ||
enc_cfg->g_timebase.num !=
app_input->input_ctx[i].framerate.denominator ||
enc_cfg->g_timebase.den !=
app_input->input_ctx[i].framerate.numerator) {
die("Error: Input file dimensions and/or frame rate mismatch");
}
}
} if (enc_cfg->g_w == 0 || enc_cfg->g_h == 0) {
die("Error: Input file dimensions not set, use -w and -h");
}
// For rate control encoding stats. struct RateControlMetrics { // Number of input frames per layer. int layer_input_frames[AOM_MAX_TS_LAYERS]; // Number of encoded non-key frames per layer. int layer_enc_frames[AOM_MAX_TS_LAYERS]; // Framerate per layer layer (cumulative). double layer_framerate[AOM_MAX_TS_LAYERS]; // Target average frame size per layer (per-frame-bandwidth per layer). double layer_pfb[AOM_MAX_LAYERS]; // Actual average frame size per layer. double layer_avg_frame_size[AOM_MAX_LAYERS]; // Average rate mismatch per layer (|target - actual| / target). double layer_avg_rate_mismatch[AOM_MAX_LAYERS]; // Actual encoding bitrate per layer (cumulative across temporal layers). double layer_encoding_bitrate[AOM_MAX_LAYERS]; // Average of the short-time encoder actual bitrate. // TODO(marpan): Should we add these short-time stats for each layer? double avg_st_encoding_bitrate; // Variance of the short-time encoder actual bitrate. double variance_st_encoding_bitrate; // Window (number of frames) for computing short-timee encoding bitrate. int window_size; // Number of window measurements. int window_count; int layer_target_bitrate[AOM_MAX_LAYERS];
};
staticconstint REF_FRAMES = 8;
staticconstint INTER_REFS_PER_FRAME = 7;
// Reference frames used in this example encoder. enum {
SVC_LAST_FRAME = 0,
SVC_LAST2_FRAME,
SVC_LAST3_FRAME,
SVC_GOLDEN_FRAME,
SVC_BWDREF_FRAME,
SVC_ALTREF2_FRAME,
SVC_ALTREF_FRAME
};
// Note: these rate control metrics assume only 1 key frame in the // sequence (i.e., first frame only). So for temporal pattern# 7 // (which has key frame for every frame on base layer), the metrics // computation will be off/wrong. // TODO(marpan): Update these metrics to account for multiple key frames // in the stream. staticvoid set_rate_control_metrics(struct RateControlMetrics *rc, double framerate, int ss_number_layers, int ts_number_layers) { int ts_rate_decimator[AOM_MAX_TS_LAYERS] = { 1 };
ts_rate_decimator[0] = 1; if (ts_number_layers == 2) {
ts_rate_decimator[0] = 2;
ts_rate_decimator[1] = 1;
} if (ts_number_layers == 3) {
ts_rate_decimator[0] = 4;
ts_rate_decimator[1] = 2;
ts_rate_decimator[2] = 1;
} // Set the layer (cumulative) framerate and the target layer (non-cumulative) // per-frame-bandwidth, for the rate control encoding stats below. for (int sl = 0; sl < ss_number_layers; ++sl) { int i = sl * ts_number_layers;
rc->layer_framerate[0] = framerate / ts_rate_decimator[0];
rc->layer_pfb[i] =
1000.0 * rc->layer_target_bitrate[i] / rc->layer_framerate[0]; for (int tl = 0; tl < ts_number_layers; ++tl) {
i = sl * ts_number_layers + tl; if (tl > 0) {
rc->layer_framerate[tl] = framerate / ts_rate_decimator[tl];
rc->layer_pfb[i] =
1000.0 *
(rc->layer_target_bitrate[i] - rc->layer_target_bitrate[i - 1]) /
(rc->layer_framerate[tl] - rc->layer_framerate[tl - 1]);
}
rc->layer_input_frames[tl] = 0;
rc->layer_enc_frames[tl] = 0;
rc->layer_encoding_bitrate[i] = 0.0;
rc->layer_avg_frame_size[i] = 0.0;
rc->layer_avg_rate_mismatch[i] = 0.0;
}
}
rc->window_count = 0;
rc->window_size = 15;
rc->avg_st_encoding_bitrate = 0.0;
rc->variance_st_encoding_bitrate = 0.0;
}
staticvoid printout_rate_control_summary(struct RateControlMetrics *rc, int frame_cnt, int ss_number_layers, int ts_number_layers) { int tot_num_frames = 0; double perc_fluctuation = 0.0;
printf("Total number of processed frames: %d\n\n", frame_cnt - 1);
printf("Rate control layer stats for %d layer(s):\n\n", ts_number_layers); for (int sl = 0; sl < ss_number_layers; ++sl) {
tot_num_frames = 0; for (int tl = 0; tl < ts_number_layers; ++tl) { int i = sl * ts_number_layers + tl; constint num_dropped =
tl > 0 ? rc->layer_input_frames[tl] - rc->layer_enc_frames[tl]
: rc->layer_input_frames[tl] - rc->layer_enc_frames[tl] - 1;
tot_num_frames += rc->layer_input_frames[tl];
rc->layer_encoding_bitrate[i] = 0.001 * rc->layer_framerate[tl] *
rc->layer_encoding_bitrate[i] /
tot_num_frames;
rc->layer_avg_frame_size[i] =
rc->layer_avg_frame_size[i] / rc->layer_enc_frames[tl];
rc->layer_avg_rate_mismatch[i] =
100.0 * rc->layer_avg_rate_mismatch[i] / rc->layer_enc_frames[tl];
printf("For layer#: %d %d \n", sl, tl);
printf("Bitrate (target vs actual): %d %f\n", rc->layer_target_bitrate[i],
rc->layer_encoding_bitrate[i]);
printf("Average frame size (target vs actual): %f %f\n", rc->layer_pfb[i],
rc->layer_avg_frame_size[i]);
printf("Average rate_mismatch: %f\n", rc->layer_avg_rate_mismatch[i]);
printf( "Number of input frames, encoded (non-key) frames, " "and perc dropped frames: %d %d %f\n",
rc->layer_input_frames[tl], rc->layer_enc_frames[tl],
100.0 * num_dropped / rc->layer_input_frames[tl]);
printf("\n");
}
}
rc->avg_st_encoding_bitrate = rc->avg_st_encoding_bitrate / rc->window_count;
rc->variance_st_encoding_bitrate =
rc->variance_st_encoding_bitrate / rc->window_count -
(rc->avg_st_encoding_bitrate * rc->avg_st_encoding_bitrate);
perc_fluctuation = 100.0 * sqrt(rc->variance_st_encoding_bitrate) /
rc->avg_st_encoding_bitrate;
printf("Short-time stats, for window of %d frames:\n", rc->window_size);
printf("Average, rms-variance, and percent-fluct: %f %f %f\n",
rc->avg_st_encoding_bitrate, sqrt(rc->variance_st_encoding_bitrate),
perc_fluctuation); if (frame_cnt - 1 != tot_num_frames)
die("Error: Number of input frames not equal to output!\n");
}
// Layer pattern configuration. staticvoid set_layer_pattern( int layering_mode, int superframe_cnt, aom_svc_layer_id_t *layer_id,
aom_svc_ref_frame_config_t *ref_frame_config,
aom_svc_ref_frame_comp_pred_t *ref_frame_comp_pred, int *use_svc_control, int spatial_layer_id, int is_key_frame, int ksvc_mode, int speed) { // Setting this flag to 1 enables simplex example of // RPS (Reference Picture Selection) for 1 layer. int use_rps_example = 0; int i; int enable_longterm_temporal_ref = 1; int shift = (layering_mode == 8) ? 2 : 0; int simulcast_mode = (layering_mode == 11);
*use_svc_control = 1;
layer_id->spatial_layer_id = spatial_layer_id; int lag_index = 0; int base_count = superframe_cnt >> 2;
ref_frame_comp_pred->use_comp_pred[0] = 0; // GOLDEN_LAST
ref_frame_comp_pred->use_comp_pred[1] = 0; // LAST2_LAST
ref_frame_comp_pred->use_comp_pred[2] = 0; // ALTREF_LAST // Set the reference map buffer idx for the 7 references: // LAST_FRAME (0), LAST2_FRAME(1), LAST3_FRAME(2), GOLDEN_FRAME(3), // BWDREF_FRAME(4), ALTREF2_FRAME(5), ALTREF_FRAME(6). for (i = 0; i < INTER_REFS_PER_FRAME; i++) ref_frame_config->ref_idx[i] = i; for (i = 0; i < INTER_REFS_PER_FRAME; i++) ref_frame_config->reference[i] = 0; for (i = 0; i < REF_FRAMES; i++) ref_frame_config->refresh[i] = 0;
if (ksvc_mode) { // Same pattern as case 9, but the reference strucutre will be constrained // below.
layering_mode = 9;
} switch (layering_mode) { case 0: if (use_rps_example == 0) { // 1-layer: update LAST on every frame, reference LAST.
layer_id->temporal_layer_id = 0;
layer_id->spatial_layer_id = 0;
ref_frame_config->refresh[0] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} else { // Pattern of 2 references (ALTREF and GOLDEN) trailing // LAST by 4 and 8 frames, with some switching logic to // sometimes only predict from the longer-term reference //(golden here). This is simple example to test RPS // (reference picture selection). int last_idx = 0; int last_idx_refresh = 0; int gld_idx = 0; int alt_ref_idx = 0; int lag_alt = 4; int lag_gld = 8;
layer_id->temporal_layer_id = 0;
layer_id->spatial_layer_id = 0; int sh = 8; // slots 0 - 7. // Moving index slot for last: 0 - (sh - 1) if (superframe_cnt > 1) last_idx = (superframe_cnt - 1) % sh; // Moving index for refresh of last: one ahead for next frame.
last_idx_refresh = superframe_cnt % sh; // Moving index for gld_ref, lag behind current by lag_gld if (superframe_cnt > lag_gld) gld_idx = (superframe_cnt - lag_gld) % sh; // Moving index for alt_ref, lag behind LAST by lag_alt frames. if (superframe_cnt > lag_alt)
alt_ref_idx = (superframe_cnt - lag_alt) % sh; // Set the ref_idx. // Default all references to slot for last. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = last_idx; // Set the ref_idx for the relevant references.
ref_frame_config->ref_idx[SVC_LAST_FRAME] = last_idx;
ref_frame_config->ref_idx[SVC_LAST2_FRAME] = last_idx_refresh;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = gld_idx;
ref_frame_config->ref_idx[SVC_ALTREF_FRAME] = alt_ref_idx; // Refresh this slot, which will become LAST on next frame.
ref_frame_config->refresh[last_idx_refresh] = 1; // Reference LAST, ALTREF, and GOLDEN
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
ref_frame_config->reference[SVC_ALTREF_FRAME] = 1;
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1; // Switch to only GOLDEN every 300 frames. if (superframe_cnt % 200 == 0 && superframe_cnt > 0) {
ref_frame_config->reference[SVC_LAST_FRAME] = 0;
ref_frame_config->reference[SVC_ALTREF_FRAME] = 0;
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1; // Test if the long-term is LAST instead, this is just a renaming // but its tests if encoder behaves the same, whether its // LAST or GOLDEN. if (superframe_cnt % 400 == 0 && superframe_cnt > 0) {
ref_frame_config->ref_idx[SVC_LAST_FRAME] = gld_idx;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
ref_frame_config->reference[SVC_ALTREF_FRAME] = 0;
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 0;
}
}
} break; case 1: // 2-temporal layer. // 1 3 5 // 0 2 4 // Keep golden fixed at slot 3.
base_count = superframe_cnt >> 1;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3; // Cyclically refresh slots 5, 6, 7, for lag alt ref.
lag_index = 5; if (base_count > 0) {
lag_index = 5 + (base_count % 3); if (superframe_cnt % 2 != 0) lag_index = 5 + ((base_count + 1) % 3);
} // Set the altref slot to lag_index.
ref_frame_config->ref_idx[SVC_ALTREF_FRAME] = lag_index; if (superframe_cnt % 2 == 0) {
layer_id->temporal_layer_id = 0; // Update LAST on layer 0, reference LAST.
ref_frame_config->refresh[0] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1; // Refresh lag_index slot, needed for lagging golen.
ref_frame_config->refresh[lag_index] = 1; // Refresh GOLDEN every x base layer frames. if (base_count % 32 == 0) ref_frame_config->refresh[3] = 1;
} else {
layer_id->temporal_layer_id = 1; // No updates on layer 1, reference LAST (TL0).
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} // Always reference golden and altref on TL0. if (layer_id->temporal_layer_id == 0) {
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1;
ref_frame_config->reference[SVC_ALTREF_FRAME] = 1;
} break; case 2: // 3-temporal layer: // 1 3 5 7 // 2 6 // 0 4 8 if (superframe_cnt % 4 == 0) { // Base layer.
layer_id->temporal_layer_id = 0; // Update LAST on layer 0, reference LAST.
ref_frame_config->refresh[0] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 1) % 4 == 0) {
layer_id->temporal_layer_id = 2; // First top layer: no updates, only reference LAST (TL0).
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 2) % 4 == 0) {
layer_id->temporal_layer_id = 1; // Middle layer (TL1): update LAST2, only reference LAST (TL0).
ref_frame_config->refresh[1] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 3) % 4 == 0) {
layer_id->temporal_layer_id = 2; // Second top layer: no updates, only reference LAST. // Set buffer idx for LAST to slot 1, since that was the slot // updated in previous frame. So LAST is TL1 frame.
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->ref_idx[SVC_LAST2_FRAME] = 0;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} break; case 3: // 3 TL, same as above, except allow for predicting // off 2 more references (GOLDEN and ALTREF), with // GOLDEN updated periodically, and ALTREF lagging from // LAST from ~4 frames. Both GOLDEN and ALTREF // can only be updated on base temporal layer.
// Keep golden fixed at slot 3.
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3; // Cyclically refresh slots 5, 6, 7, for lag altref.
lag_index = 5; if (base_count > 0) {
lag_index = 5 + (base_count % 3); if (superframe_cnt % 4 != 0) lag_index = 5 + ((base_count + 1) % 3);
} // Set the altref slot to lag_index.
ref_frame_config->ref_idx[SVC_ALTREF_FRAME] = lag_index; if (superframe_cnt % 4 == 0) { // Base layer.
layer_id->temporal_layer_id = 0; // Update LAST on layer 0, reference LAST.
ref_frame_config->refresh[0] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1; // Refresh GOLDEN every x ~10 base layer frames. if (base_count % 10 == 0) ref_frame_config->refresh[3] = 1; // Refresh lag_index slot, needed for lagging altref.
ref_frame_config->refresh[lag_index] = 1;
} elseif ((superframe_cnt - 1) % 4 == 0) {
layer_id->temporal_layer_id = 2; // First top layer: no updates, only reference LAST (TL0).
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 2) % 4 == 0) {
layer_id->temporal_layer_id = 1; // Middle layer (TL1): update LAST2, only reference LAST (TL0).
ref_frame_config->refresh[1] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 3) % 4 == 0) {
layer_id->temporal_layer_id = 2; // Second top layer: no updates, only reference LAST. // Set buffer idx for LAST to slot 1, since that was the slot // updated in previous frame. So LAST is TL1 frame.
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->ref_idx[SVC_LAST2_FRAME] = 0;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} // Every frame can reference GOLDEN AND ALTREF.
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1;
ref_frame_config->reference[SVC_ALTREF_FRAME] = 1; // Allow for compound prediction for LAST-ALTREF and LAST-GOLDEN. if (speed >= 7) {
ref_frame_comp_pred->use_comp_pred[2] = 1;
ref_frame_comp_pred->use_comp_pred[0] = 1;
} break; case 4: // 3-temporal layer: but middle layer updates GF, so 2nd TL2 will // only reference GF (not LAST). Other frames only reference LAST. // 1 3 5 7 // 2 6 // 0 4 8 if (superframe_cnt % 4 == 0) { // Base layer.
layer_id->temporal_layer_id = 0; // Update LAST on layer 0, only reference LAST.
ref_frame_config->refresh[0] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 1) % 4 == 0) {
layer_id->temporal_layer_id = 2; // First top layer: no updates, only reference LAST (TL0).
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 2) % 4 == 0) {
layer_id->temporal_layer_id = 1; // Middle layer (TL1): update GF, only reference LAST (TL0).
ref_frame_config->refresh[3] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif ((superframe_cnt - 3) % 4 == 0) {
layer_id->temporal_layer_id = 2; // Second top layer: no updates, only reference GF.
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1;
} break; case 5: // 2 spatial layers, 1 temporal.
layer_id->temporal_layer_id = 0; if (layer_id->spatial_layer_id == 0) { // Reference LAST, update LAST.
ref_frame_config->refresh[0] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 1 // and GOLDEN to slot 0. Update slot 1 (LAST).
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 0;
ref_frame_config->refresh[1] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1;
} break; case 6: // 3 spatial layers, 1 temporal. // Note for this case, we set the buffer idx for all references to be // either LAST or GOLDEN, which are always valid references, since decoder // will check if any of the 7 references is valid scale in // valid_ref_frame_size().
layer_id->temporal_layer_id = 0; if (layer_id->spatial_layer_id == 0) { // Reference LAST, update LAST. Set all buffer_idx to 0. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->refresh[0] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 1 // and GOLDEN (and all other refs) to slot 0. // Update slot 1 (LAST). for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->refresh[1] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 2 // and GOLDEN (and all other refs) to slot 1. // Update slot 2 (LAST). for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 1;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
ref_frame_config->refresh[2] = 1;
ref_frame_config->reference[SVC_LAST_FRAME] = 1;
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1; // For 3 spatial layer case: allow for top spatial layer to use // additional temporal reference. Update every 10 frames. if (enable_longterm_temporal_ref) {
ref_frame_config->ref_idx[SVC_ALTREF_FRAME] = REF_FRAMES - 1;
ref_frame_config->reference[SVC_ALTREF_FRAME] = 1; if (base_count % 10 == 0)
ref_frame_config->refresh[REF_FRAMES - 1] = 1;
}
} break; case 7: // 2 spatial and 3 temporal layer.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; if (superframe_cnt % 4 == 0) { // Base temporal layer
layer_id->temporal_layer_id = 0; if (layer_id->spatial_layer_id == 0) { // Reference LAST, update LAST // Set all buffer_idx to 0 for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->refresh[0] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->refresh[1] = 1;
}
} elseif ((superframe_cnt - 1) % 4 == 0) { // First top temporal enhancement layer.
layer_id->temporal_layer_id = 2; if (layer_id->spatial_layer_id == 0) { for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3;
ref_frame_config->refresh[3] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 1, // GOLDEN (and all other refs) to slot 3. // No update. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 3;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
}
} elseif ((superframe_cnt - 2) % 4 == 0) { // Middle temporal enhancement layer.
layer_id->temporal_layer_id = 1; if (layer_id->spatial_layer_id == 0) { // Reference LAST. // Set all buffer_idx to 0. // Set GOLDEN to slot 5 and update slot 5. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 5 - shift;
ref_frame_config->refresh[5 - shift] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 1, // GOLDEN (and all other refs) to slot 5. // Set LAST3 to slot 6 and update slot 6. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 5 - shift;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->ref_idx[SVC_LAST3_FRAME] = 6 - shift;
ref_frame_config->refresh[6 - shift] = 1;
}
} elseif ((superframe_cnt - 3) % 4 == 0) { // Second top temporal enhancement layer.
layer_id->temporal_layer_id = 2; if (layer_id->spatial_layer_id == 0) { // Set LAST to slot 5 and reference LAST. // Set GOLDEN to slot 3 and update slot 3. // Set all other buffer_idx to 0. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 5 - shift;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3;
ref_frame_config->refresh[3] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 6, // GOLDEN to slot 3. No update. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 6 - shift;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3;
}
} break; case 8: // 3 spatial and 3 temporal layer. // Same as case 9 but overalap in the buffer slot updates. // (shift = 2). The slots 3 and 4 updated by first TL2 are // reused for update in TL1 superframe. // Note for this case, frame order hint must be disabled for // lower resolutios (operating points > 0) to be decoedable. case 9: // 3 spatial and 3 temporal layer. // No overlap in buffer updates between TL2 and TL1. // TL2 updates slot 3 and 4, TL1 updates 5, 6, 7. // Set the references via the svc_ref_frame_config control. // Always reference LAST.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; if (superframe_cnt % 4 == 0) { // Base temporal layer.
layer_id->temporal_layer_id = 0; if (layer_id->spatial_layer_id == 0) { // Reference LAST, update LAST. // Set all buffer_idx to 0. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->refresh[0] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 1, // GOLDEN (and all other refs) to slot 0. // Update slot 1 (LAST). for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->refresh[1] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 2, // GOLDEN (and all other refs) to slot 1. // Update slot 2 (LAST). for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 1;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
ref_frame_config->refresh[2] = 1;
}
} elseif ((superframe_cnt - 1) % 4 == 0) { // First top temporal enhancement layer.
layer_id->temporal_layer_id = 2; if (layer_id->spatial_layer_id == 0) { // Reference LAST (slot 0). // Set GOLDEN to slot 3 and update slot 3. // Set all other buffer_idx to slot 0. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3;
ref_frame_config->refresh[3] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 1, // GOLDEN (and all other refs) to slot 3. // Set LAST2 to slot 4 and Update slot 4. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 3;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->ref_idx[SVC_LAST2_FRAME] = 4;
ref_frame_config->refresh[4] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 2, // GOLDEN (and all other refs) to slot 4. // No update. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 4;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
}
} elseif ((superframe_cnt - 2) % 4 == 0) { // Middle temporal enhancement layer.
layer_id->temporal_layer_id = 1; if (layer_id->spatial_layer_id == 0) { // Reference LAST. // Set all buffer_idx to 0. // Set GOLDEN to slot 5 and update slot 5. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 5 - shift;
ref_frame_config->refresh[5 - shift] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 1, // GOLDEN (and all other refs) to slot 5. // Set LAST3 to slot 6 and update slot 6. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 5 - shift;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
ref_frame_config->ref_idx[SVC_LAST3_FRAME] = 6 - shift;
ref_frame_config->refresh[6 - shift] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 2, // GOLDEN (and all other refs) to slot 6. // Set LAST3 to slot 7 and update slot 7. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 6 - shift;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
ref_frame_config->ref_idx[SVC_LAST3_FRAME] = 7 - shift;
ref_frame_config->refresh[7 - shift] = 1;
}
} elseif ((superframe_cnt - 3) % 4 == 0) { // Second top temporal enhancement layer.
layer_id->temporal_layer_id = 2; if (layer_id->spatial_layer_id == 0) { // Set LAST to slot 5 and reference LAST. // Set GOLDEN to slot 3 and update slot 3. // Set all other buffer_idx to 0. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 5 - shift;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3;
ref_frame_config->refresh[3] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 6, // GOLDEN to slot 3. Set LAST2 to slot 4 and update slot 4. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 6 - shift;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3;
ref_frame_config->ref_idx[SVC_LAST2_FRAME] = 4;
ref_frame_config->refresh[4] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // Reference LAST and GOLDEN. Set buffer_idx for LAST to slot 7, // GOLDEN to slot 4. No update. for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 7 - shift;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 4;
}
} break; case 11: // Simulcast mode for 3 spatial and 3 temporal layers. // No inter-layer predicton, only prediction is temporal and single // reference (LAST). // No overlap in buffer slots between spatial layers. So for example, // SL0 only uses slots 0 and 1. // SL1 only uses slots 2 and 3. // SL2 only uses slots 4 and 5. // All 7 references for each inter-frame must only access buffer slots // for that spatial layer. // On key (super)frames: SL1 and SL2 must have no references set // and must refresh all the slots for that layer only (so 2 and 3 // for SL1, 4 and 5 for SL2). The base SL0 will be labelled internally // as a Key frame (refresh all slots). SL1/SL2 will be labelled // internally as Intra-only frames that allow that stream to be decoded. // These conditions will allow for each spatial stream to be // independently decodeable.
// Initialize all references to 0 (don't use reference). for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->reference[i] = 0; // Initialize as no refresh/update for all slots. for (i = 0; i < REF_FRAMES; i++) ref_frame_config->refresh[i] = 0; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
if (is_key_frame) { if (layer_id->spatial_layer_id == 0) { // Assign LAST/GOLDEN to slot 0/1. // Refesh slots 0 and 1 for SL0. // SL0: this will get set to KEY frame internally.
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 0;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 1;
ref_frame_config->refresh[0] = 1;
ref_frame_config->refresh[1] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // Assign LAST/GOLDEN to slot 2/3. // Refesh slots 2 and 3 for SL1. // This will get set to Intra-only frame internally.
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 3;
ref_frame_config->refresh[2] = 1;
ref_frame_config->refresh[3] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // Assign LAST/GOLDEN to slot 4/5. // Refresh slots 4 and 5 for SL2. // This will get set to Intra-only frame internally.
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 4;
ref_frame_config->ref_idx[SVC_GOLDEN_FRAME] = 5;
ref_frame_config->refresh[4] = 1;
ref_frame_config->refresh[5] = 1;
}
} elseif (superframe_cnt % 4 == 0) { // Base temporal layer: TL0
layer_id->temporal_layer_id = 0; if (layer_id->spatial_layer_id == 0) { // SL0 // Reference LAST. Assign all references to either slot // 0 or 1. Here we assign LAST to slot 0, all others to 1. // Update slot 0 (LAST).
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 1;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 0;
ref_frame_config->refresh[0] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // SL1 // Reference LAST. Assign all references to either slot // 2 or 3. Here we assign LAST to slot 2, all others to 3. // Update slot 2 (LAST).
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 3;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
ref_frame_config->refresh[2] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // SL2 // Reference LAST. Assign all references to either slot // 4 or 5. Here we assign LAST to slot 4, all others to 5. // Update slot 4 (LAST).
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 5;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 4;
ref_frame_config->refresh[4] = 1;
}
} elseif ((superframe_cnt - 1) % 4 == 0) { // First top temporal enhancement layer: TL2
layer_id->temporal_layer_id = 2; if (layer_id->spatial_layer_id == 0) { // SL0 // Reference LAST (slot 0). Assign other references to slot 1. // No update/refresh on any slots.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 1;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 0;
} elseif (layer_id->spatial_layer_id == 1) { // SL1 // Reference LAST (slot 2). Assign other references to slot 3. // No update/refresh on any slots.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 3;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
} elseif (layer_id->spatial_layer_id == 2) { // SL2 // Reference LAST (slot 4). Assign other references to slot 4. // No update/refresh on any slots.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 5;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 4;
}
} elseif ((superframe_cnt - 2) % 4 == 0) { // Middle temporal enhancement layer: TL1
layer_id->temporal_layer_id = 1; if (layer_id->spatial_layer_id == 0) { // SL0 // Reference LAST (slot 0). // Set GOLDEN to slot 1 and update slot 1. // This will be used as reference for next TL2.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 1;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 0;
ref_frame_config->refresh[1] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // SL1 // Reference LAST (slot 2). // Set GOLDEN to slot 3 and update slot 3. // This will be used as reference for next TL2.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 3;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 2;
ref_frame_config->refresh[3] = 1;
} elseif (layer_id->spatial_layer_id == 2) { // SL2 // Reference LAST (slot 4). // Set GOLDEN to slot 5 and update slot 5. // This will be used as reference for next TL2.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 5;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 4;
ref_frame_config->refresh[5] = 1;
}
} elseif ((superframe_cnt - 3) % 4 == 0) { // Second top temporal enhancement layer: TL2
layer_id->temporal_layer_id = 2; if (layer_id->spatial_layer_id == 0) { // SL0 // Reference LAST (slot 1). Assign other references to slot 0. // No update/refresh on any slots.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 0;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 1;
} elseif (layer_id->spatial_layer_id == 1) { // SL1 // Reference LAST (slot 3). Assign other references to slot 2. // No update/refresh on any slots.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 2;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 3;
} elseif (layer_id->spatial_layer_id == 2) { // SL2 // Reference LAST (slot 5). Assign other references to slot 4. // No update/refresh on any slots.
ref_frame_config->reference[SVC_LAST_FRAME] = 1; for (i = 0; i < INTER_REFS_PER_FRAME; i++)
ref_frame_config->ref_idx[i] = 4;
ref_frame_config->ref_idx[SVC_LAST_FRAME] = 5;
}
} if (!simulcast_mode && layer_id->spatial_layer_id > 0) { // Always reference GOLDEN (inter-layer prediction).
ref_frame_config->reference[SVC_GOLDEN_FRAME] = 1; if (ksvc_mode) { // KSVC: only keep the inter-layer reference (GOLDEN) for // superframes whose base is key. if (!is_key_frame) ref_frame_config->reference[SVC_GOLDEN_FRAME] = 0;
} if (is_key_frame && layer_id->spatial_layer_id > 1) { // On superframes whose base is key: remove LAST to avoid prediction // off layer two levels below.
ref_frame_config->reference[SVC_LAST_FRAME] = 0;
}
} // For 3 spatial layer case 8 (where there is free buffer slot): // allow for top spatial layer to use additional temporal reference. // Additional reference is only updated on base temporal layer, every // 10 TL0 frames here. if (!simulcast_mode && enable_longterm_temporal_ref &&
layer_id->spatial_layer_id == 2 && layering_mode == 8) {
ref_frame_config->ref_idx[SVC_ALTREF_FRAME] = REF_FRAMES - 1; if (!is_key_frame) ref_frame_config->reference[SVC_ALTREF_FRAME] = 1; if (base_count % 10 == 0 && layer_id->temporal_layer_id == 0)
ref_frame_config->refresh[REF_FRAMES - 1] = 1;
} break; default: assert(0); die("Error: Unsupported temporal layering mode!\n");
}
}
staticvoid write_literal(struct aom_write_bit_buffer *wb, uint32_t data,
uint8_t bits, uint32_t offset = 0) { if (bits > 32) {
die("Invalid bits value %d > 32\n", bits);
} const uint32_t max = static_cast<uint32_t>(((uint64_t)1 << bits) - 1); if (data < offset || (data - offset) > max) {
die("Invalid data, value %u out of range [%u, %" PRIu64 "]\n", data, offset,
(uint64_t)max + offset);
}
aom_wb_write_unsigned_literal(wb, data - offset, bits);
}
staticvoid add_multilayer_metadata(
aom_image_t *frame, const libaom_examples::MultilayerMetadata &multilayer) { // Pretty large buffer to accommodate the largest multilayer metadata // possible, with 4 alpha segmentation layers (each can be up to about 66kB).
std::vector<uint8_t> data(66000 * multilayer.layers.size()); struct aom_write_bit_buffer buffer = { data.data(), 0 };
write_literal(&buffer, multilayer.use_case, 6); if (multilayer.layers.empty()) {
die("Invalid multilayer metadata, no layers found\n");
} elseif (multilayer.layers.size() > MAX_NUM_SPATIAL_LAYERS) {
die("Invalid multilayer metadata, too many layers (max is %d)\n",
MAX_NUM_SPATIAL_LAYERS);
}
write_literal(&buffer, (int)multilayer.layers.size() - 1, 2);
assert(buffer.bit_offset % 8 == 0); for (size_t i = 0; i < multilayer.layers.size(); ++i) { const libaom_examples::LayerMetadata &layer = multilayer.layers[i]; // Alpha info with segmentation with labels can be up to about 66k bytes, // which requires 3 bytes to encode in leb128. constint bytes_reserved_for_size = 3; // Placeholder for layer_metadata_size which will be written later.
write_literal(&buffer, 0, bytes_reserved_for_size * 8); const uint32_t metadata_start = buffer.bit_offset;
write_literal(&buffer, (int)i, 2); // ml_spatial_id
write_literal(&buffer, layer.layer_type, 5);
write_literal(&buffer, layer.luma_plane_only_flag, 1);
write_literal(&buffer, layer.layer_view_type, 3);
write_literal(&buffer, layer.group_id, 2);
write_literal(&buffer, layer.layer_dependency_idc, 3);
write_literal(&buffer, layer.layer_metadata_scope, 2);
write_literal(&buffer, 0, 4); // ml_reserved_4bits
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