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avcodec/libfdk-aacdec: properly handle decoder delay

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Shift timestamps when available, and take into account the caller requested
samples to be discarded alongside the decoder delay.

Should fix issue #24526.

Signed-off-by: James Almer <jamrial@gmail.com>
This commit is contained in:
James Almer
2026-09-15 22:35:25 -03:00
parent 49fb9b44d5
commit c8595be8e6
1 changed files with 71 additions and 7 deletions
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78
libavcodec/libfdk-aacdec.c
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@@ -21,6 +21,7 @@
#include "libavutil/channel_layout.h"
#include "libavutil/common.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/mem.h"
#include "libavutil/opt.h"
#include "avcodec.h"
@@ -63,7 +64,12 @@ typedef struct FDKAACDecContext {
#if FDKDEC_VER_AT_LEAST(2, 5) // 2.5.10
int output_delay_set;
int flush_samples;
int skip_samples;
int delay_samples;
int output_delay;
int discard_padding;
int64_t last_pts;
int64_t last_dts;
#endif
AVChannelLayout downmix_layout;
} FDKAACDecContext;
@@ -138,6 +144,10 @@ static int get_stream_info(AVCodecContext *avctx, AVFrame *frame)
// Set this only once.
s->flush_samples = info->outputDelay;
s->delay_samples = info->outputDelay;
s->skip_samples = info->outputDelay;
s->output_delay = info->outputDelay;
s->last_pts = AV_NOPTS_VALUE;
s->last_dts = AV_NOPTS_VALUE;
s->output_delay_set = 1;
}
#endif
@@ -503,19 +513,76 @@ static int fdk_aac_decode_frame(AVCodecContext *avctx, AVFrame *frame,
goto end;
frame->nb_samples = avctx->frame_size;
if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
goto end;
#if FDKDEC_VER_AT_LEAST(2, 5) // 2.5.10
if (flags & AACDEC_FLUSH) {
if (s->last_pts != AV_NOPTS_VALUE)
frame->pts = av_sat_add64(s->last_pts,
av_rescale_q(frame->nb_samples, avctx->time_base,
(AVRational){ 1, avctx->sample_rate }));
if (s->last_dts != AV_NOPTS_VALUE)
frame->pkt_dts = av_sat_add64(s->last_dts,
av_rescale_q(frame->nb_samples, avctx->time_base,
(AVRational){ 1, avctx->sample_rate }));
// Only return the right amount of samples at the end; if calling the
// decoder with AACDEC_FLUSH, it will keep returning frames indefinitely.
frame->nb_samples = FFMIN(s->flush_samples, frame->nb_samples);
av_log(s, AV_LOG_DEBUG, "Returning %d/%d delayed samples.\n",
frame->nb_samples, s->flush_samples);
if (s->skip_samples || s->discard_padding) {
AVFrameSideData *sd = av_frame_get_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES);
if (!sd) {
sd = av_frame_new_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES, 10);
if (sd)
memset(sd->data, 0, 10);
}
if (sd && sd->size >= 10) {
AV_WL32(sd->data, s->skip_samples);
AV_WL32(sd->data + 4, s->discard_padding);
}
s->skip_samples = 0;
s->discard_padding = 0;
}
s->flush_samples -= frame->nb_samples;
s->last_pts = frame->pts;
s->last_dts = frame->pkt_dts;
} else {
// Trim off samples from the start to compensate for extra decoder
// delay. We could also just adjust the pts, but this avoids
// including the extra samples in the output altogether.
if (s->delay_samples) {
AVFrameSideData *sd = av_frame_get_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES);
if (!sd && s->skip_samples) {
sd = av_frame_new_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES, 10);
if (sd)
memset(sd->data, 0, 10);
}
if (sd && sd->size >= 10) {
int skip_samples = AV_RL32(sd->data);
s->discard_padding = AV_RL32(sd->data + 4);
if (s->discard_padding >= s->output_delay) {
AV_WL32(sd->data + 4, s->discard_padding - s->output_delay);
s->discard_padding = s->output_delay;
} else
AV_WL32(sd->data + 4, 0);
AV_WL32(sd->data, skip_samples + s->skip_samples);
s->skip_samples = 0;
}
if (frame->pts != AV_NOPTS_VALUE && s->output_delay) {
frame->pts = av_sat_sub64(frame->pts,
av_rescale_q(s->output_delay,
(AVRational){ 1, avctx->sample_rate },
avctx->time_base));
if (frame->pkt_dts != AV_NOPTS_VALUE && s->output_delay)
frame->pkt_dts = av_sat_sub64(frame->pkt_dts,
av_rescale_q(s->output_delay,
(AVRational){ 1, avctx->sample_rate },
avctx->time_base));
s->delay_samples = 0;
s->last_pts = frame->pts;
s->last_dts = frame->pkt_dts;
} else if (s->delay_samples) {
// Trim off samples from the start to compensate for extra decoder
// delay, in the absense of timestamps.
int drop_samples = FFMIN(s->delay_samples, frame->nb_samples);
av_log(s, AV_LOG_DEBUG, "Dropping %d/%d delayed samples.\n",
drop_samples, s->delay_samples);
@@ -528,9 +595,6 @@ static int fdk_aac_decode_frame(AVCodecContext *avctx, AVFrame *frame,
}
#endif
if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
goto end;
memcpy(frame->extended_data[0], s->decoder_buffer + input_offset,
avctx->ch_layout.nb_channels * frame->nb_samples *
av_get_bytes_per_sample(avctx->sample_fmt));