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fftools/ffmpeg: change video decoding timestamp generation

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When no timestamps are available from the container, the video decoding
code will currently use fake dts values - generated in
process_input_packet() based on a combination of information from the
decoder and the parser (obtained via the demuxer) - to generate
timestamps during decoder flushing. This is fragile, hard to follow, and
unnecessarily convoluted, since more reliable information can be
obtained directly from post-decoding values.

The new code keeps track of the last decoded frame pts and estimates its
duration based on a number of heuristics. Timestamps generated when both
pts and pkt_dts are missing are then simple pts+duration of the last frame.
The heuristics are somewhat complicated by the fact that lavf insists on
making up packet timestamps based on its highly incomplete information.
That should be removed in the future, allowing to further simplify this
code.

The results of the following tests change:
* h264-3386 now requires -fps_mode passthrough to avoid dropping frames
  at the end; this is a pathology of the interaction of the new and old
  code, and the fact that the sample switches from field to frame coding
  in the last packet, and will be fixed in following commits
* hevc-conformance-DELTAQP_A_BRCM_4 stops inventing an arbitrary
  timestamp gap at the end
* hevc-small422chroma - the single frame output by this test now has a
  timestamp of 0, rather than an arbitrary 7
This commit is contained in:
Anton Khirnov 2023-04-09 09:55:55 +02:00
parent 380db56928
commit 5d407cb2d7
7 changed files with 75 additions and 28 deletions
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79
fftools/ffmpeg.c
View File

@ -1275,11 +1275,63 @@ static int decode_audio(InputStream *ist, AVPacket *pkt, int *got_output,
return err < 0 ? err : ret;
}
static int64_t video_duration_estimate(const InputStream *ist, const AVFrame *frame)
{
const InputFile *ifile = input_files[ist->file_index];
const int container_nots = !!(ifile->ctx->iformat->flags & AVFMT_NOTIMESTAMPS);
int64_t codec_duration = 0;
// XXX lavf currently makes up frame durations when they are not provided by
// the container. As there is no way to reliably distinguish real container
// durations from the fake made-up ones, we use heuristics based on whether
// the container has timestamps. Eventually lavf should stop making up
// durations, then this should be simplified.
// prefer frame duration for containers with timestamps
if (frame->duration > 0 && !container_nots)
return frame->duration;
if (ist->dec_ctx->framerate.den && ist->dec_ctx->framerate.num) {
int ticks = frame->repeat_pict >= 0 ?
frame->repeat_pict + 1 :
ist->dec_ctx->ticks_per_frame;
codec_duration = av_rescale_q(ticks, av_inv_q(ist->dec_ctx->framerate),
ist->st->time_base);
}
// prefer codec-layer duration for containers without timestamps
if (codec_duration > 0 && container_nots)
return codec_duration;
// when timestamps are available, repeat last frame's actual duration
// (i.e. pts difference between this and last frame)
if (frame->pts != AV_NOPTS_VALUE && ist->last_frame_pts != AV_NOPTS_VALUE &&
frame->pts > ist->last_frame_pts)
return frame->pts - ist->last_frame_pts;
// try frame/codec duration
if (frame->duration > 0)
return frame->duration;
if (codec_duration > 0)
return codec_duration;
// try average framerate
if (ist->st->avg_frame_rate.num && ist->st->avg_frame_rate.den) {
int64_t d = av_rescale_q(1, av_inv_q(ist->st->avg_frame_rate),
ist->st->time_base);
if (d > 0)
return d;
}
// last resort is last frame's estimated duration, and 1
return FFMAX(ist->last_frame_duration_est, 1);
}
static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output, int64_t *duration_pts, int eof,
int *decode_failed)
{
AVFrame *decoded_frame = ist->decoded_frame;
int i, ret = 0, err = 0;
int ret = 0, err = 0;
int64_t best_effort_timestamp;
int64_t dts = AV_NOPTS_VALUE;
@ -1295,16 +1347,6 @@ static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output, int64_
pkt->dts = dts; // ffmpeg.c probably shouldn't do this
}
// The old code used to set dts on the drain packet, which does not work
// with the new API anymore.
if (eof) {
void *new = av_realloc_array(ist->dts_buffer, ist->nb_dts_buffer + 1, sizeof(ist->dts_buffer[0]));
if (!new)
return AVERROR(ENOMEM);
ist->dts_buffer = new;
ist->dts_buffer[ist->nb_dts_buffer++] = dts;
}
update_benchmark(NULL);
ret = decode(ist, ist->dec_ctx, decoded_frame, got_output, pkt);
update_benchmark("decode_video %d.%d", ist->file_index, ist->st->index);
@ -1363,13 +1405,10 @@ static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output, int64_
if (ist->framerate.num)
best_effort_timestamp = ist->cfr_next_pts++;
if (eof && best_effort_timestamp == AV_NOPTS_VALUE && ist->nb_dts_buffer > 0) {
best_effort_timestamp = ist->dts_buffer[0];
for (i = 0; i < ist->nb_dts_buffer - 1; i++)
ist->dts_buffer[i] = ist->dts_buffer[i + 1];
ist->nb_dts_buffer--;
}
// no timestamp available - extrapolate from previous frame duration
if (best_effort_timestamp == AV_NOPTS_VALUE &&
ist->last_frame_pts != AV_NOPTS_VALUE)
best_effort_timestamp = ist->last_frame_pts + ist->last_frame_duration_est;
if (best_effort_timestamp == AV_NOPTS_VALUE)
best_effort_timestamp = av_rescale_q(ist->pts, AV_TIME_BASE_Q, ist->st->time_base);
@ -1381,6 +1420,10 @@ static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output, int64_
ist->next_pts = ist->pts = ts;
}
// update timestamp history
ist->last_frame_duration_est = video_duration_estimate(ist, decoded_frame);
ist->last_frame_pts = decoded_frame->pts;
if (debug_ts) {
av_log(ist, AV_LOG_INFO,
"decoder -> pts:%s pts_time:%s "

9
fftools/ffmpeg.h
View File

@ -373,6 +373,12 @@ typedef struct InputStream {
/* predicted pts of the next decoded frame, in AV_TIME_BASE */
int64_t next_pts;
int64_t pts; ///< current pts of the decoded frame (in AV_TIME_BASE units)
// pts/estimated duration of the last decoded video frame
// in decoder timebase
int64_t last_frame_pts;
int64_t last_frame_duration_est;
int wrap_correction_done;
// the value of AVCodecParserContext.repeat_pict from the AVStream parser
@ -445,9 +451,6 @@ typedef struct InputStream {
uint64_t frames_decoded;
uint64_t samples_decoded;
int64_t *dts_buffer;
int nb_dts_buffer;
int got_output;
} InputStream;

3
fftools/ffmpeg_demux.c
View File

@ -532,7 +532,6 @@ static void ist_free(InputStream **pist)
av_freep(&ist->filters);
av_freep(&ist->outputs);
av_freep(&ist->hwaccel_device);
av_freep(&ist->dts_buffer);
avcodec_free_context(&ist->dec_ctx);
avcodec_parameters_free(&ist->par);
@ -879,6 +878,8 @@ static void add_input_streams(const OptionsContext *o, Demuxer *d)
ist->framerate_guessed = av_guess_frame_rate(ic, st, NULL);
ist->last_frame_pts = AV_NOPTS_VALUE;
break;
case AVMEDIA_TYPE_AUDIO: {
int guess_layout_max = INT_MAX;

2
tests/fate/h264.mak
View File

@ -444,7 +444,7 @@ fate-h264-mixed-nal-coding: CMD = framecrc -i $(TARGET_SAM
fate-h264-ref-pic-mod-overflow: CMD = framecrc -i $(TARGET_SAMPLES)/h264/ref-pic-mod-overflow.h264
fate-h264-twofields-packet: CMD = framecrc -i $(TARGET_SAMPLES)/h264/twofields_packet.mp4 -an -frames 30
fate-h264-unescaped-extradata: CMD = framecrc -i $(TARGET_SAMPLES)/h264/unescaped_extradata.mp4 -an -frames 10
fate-h264-3386: CMD = framecrc -i $(TARGET_SAMPLES)/h264/bbc2.sample.h264
fate-h264-3386: CMD = framecrc -i $(TARGET_SAMPLES)/h264/bbc2.sample.h264 -fps_mode passthrough
fate-h264-missing-frame: CMD = framecrc -i $(TARGET_SAMPLES)/h264/nondeterministic_cut.h264
fate-h264-timecode: CMD = framecrc -i $(TARGET_SAMPLES)/h264/crew_cif_timecode-2.h264

6
tests/ref/fate/h264-3386
View File

@ -47,6 +47,6 @@
0, 45, 45, 1, 2332800, 0x80b968d3
0, 46, 46, 1, 2332800, 0xa45f4e6f
0, 47, 47, 1, 2332800, 0xe0fcbade
0, 48, 48, 1, 2332800, 0x19568f4d
0, 49, 49, 1, 2332800, 0x33c53f59
0, 50, 50, 1, 2332800, 0xbdbe8fbf
0, 47, 47, 1, 2332800, 0x19568f4d
0, 48, 48, 1, 2332800, 0x33c53f59
0, 49, 49, 1, 2332800, 0xbdbe8fbf

2
tests/ref/fate/hevc-conformance-DELTAQP_A_BRCM_4
View File

@ -98,4 +98,4 @@
0, 92, 92, 1, 3133440, 0x761571be
0, 93, 93, 1, 3133440, 0x34dc14a1
0, 94, 94, 1, 3133440, 0xbb94c2d4
0, 96, 96, 1, 3133440, 0x5300e459
0, 95, 95, 1, 3133440, 0x5300e459

2
tests/ref/fate/hevc-small422chroma
View File

@ -3,4 +3,4 @@
#codec_id 0: rawvideo
#dimensions 0: 3840x2160
#sar 0: 1/1
0, 7, 7, 1, 33177600, 0x53015e18
0, 0, 0, 1, 33177600, 0x53015e18