[FFmpeg-devel] [PATCH] matroska: Set CodecDelay and SeekPreroll in the AVStream
Michael Niedermayer
michaelni at gmx.at
Thu Sep 26 14:11:56 CEST 2013
On Tue, Sep 24, 2013 at 02:50:16PM -0700, Vignesh Venkatasubramanian wrote:
> On Tue, Sep 24, 2013 at 2:14 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Sep 24, 2013 at 12:09:31PM -0700, Vignesh Venkatasubramanian wrote:
> >> On Tue, Sep 24, 2013 at 11:36 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> > On Tue, Sep 24, 2013 at 10:35:47AM -0700, Vignesh Venkatasubramanian wrote:
> >> >> On Tue, Sep 24, 2013 at 3:53 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> >> > On Mon, Sep 23, 2013 at 04:03:25PM -0700, Vignesh Venkatasubramanian wrote:
> >> >> >> On Mon, Sep 23, 2013 at 4:02 PM, Vignesh Venkatasubramanian
> >> >> >> <vigneshv at google.com> wrote:
> >> >> >> > This patch exports the values of Codec Delay and Seek Preroll
> >> >> >> > container elements as in the AVStream structure. The seek_preroll
> >> >> >> > field has been added to the AVStream struct and the minor version
> >> >> >> > of libavformat has been bumped.
> >> >> >> >
> >> >> >> > Signed-off-by: Vignesh Venkatasubramanian <vigneshv at google.com>
> >> >> >> > ---
> >> >> >> > libavformat/avformat.h | 16 ++++++++++++++++
> >> >> >> > libavformat/matroskadec.c | 14 ++++++++++++++
> >> >> >> > libavformat/version.h | 2 +-
> >> >> >> > 3 files changed, 31 insertions(+), 1 deletion(-)
> >> >> >> >
> >> >> >> > diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> >> >> >> > index b18eb3f..6671a83 100644
> >> >> >> > --- a/libavformat/avformat.h
> >> >> >> > +++ b/libavformat/avformat.h
> >> >> >> > @@ -856,6 +856,9 @@ typedef struct AVStream {
> >> >> >> >
> >> >> >> > /**
> >> >> >> > * Number of samples to skip at the start of the frame decoded from the next packet.
> >> >> >> > + *
> >> >> >> > + * Code outside avformat should access this field using:
> >> >> >> > + * av_stream_get_skip_samples/set_skip_samples(stream)
> >> >> >> > */
> >> >> >> > int skip_samples;
> >> >> >
> >> >> > when does code outside lavf need to access this ?
> >> >> >
> >> >>
> >> >> you are right. it need not be accessed outside lavf.
> >> >>
> >> >> >
> >> >> >> >
> >> >> >> > @@ -888,10 +891,23 @@ typedef struct AVStream {
> >> >> >> > */
> >> >> >> > int pts_wrap_behavior;
> >> >> >> >
> >> >> >> > + /**
> >> >> >> > + * Number of samples to skip after a discontinuity. For example, when a seek
> >> >> >> > + * happens.
> >> >> >> > + *
> >> >> >> > + * Code outside avformat should access this field using:
> >> >> >> > + * av_stream_get/set_seek_preroll(stream)
> >> >> >> > + */
> >> >> >> > + int seek_preroll;
> >> >> >> > +
> >> >> >> > } AVStream;
> >> >> >> >
> >> >> >> > AVRational av_stream_get_r_frame_rate(const AVStream *s);
> >> >> >> > void av_stream_set_r_frame_rate(AVStream *s, AVRational r);
> >> >> >> > +int av_stream_get_skip_samples(const AVStream *s);
> >> >> >> > +void av_stream_set_skip_samples(AVStream *s, int skip_samples);
> >> >> >> > +int av_stream_get_seek_preroll(const AVStream *s);
> >> >> >> > +void av_stream_set_seek_preroll(AVStream *s, int seek_preroll);
> >> >> >> >
> >> >> >> > #define AV_PROGRAM_RUNNING 1
> >> >> >> >
> >> >> >> > diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> >> >> >> > index a1b7f56..ecbc723 100644
> >> >> >> > --- a/libavformat/matroskadec.c
> >> >> >> > +++ b/libavformat/matroskadec.c
> >> >> >> > @@ -163,6 +163,8 @@ typedef struct {
> >> >> >> > uint64_t default_duration;
> >> >> >> > uint64_t flag_default;
> >> >> >> > uint64_t flag_forced;
> >> >> >> > + uint64_t codec_delay;
> >> >> >> > + uint64_t seek_preroll;
> >> >> >> > MatroskaTrackVideo video;
> >> >> >> > MatroskaTrackAudio audio;
> >> >> >> > MatroskaTrackOperation operation;
> >> >> >> > @@ -410,6 +412,8 @@ static EbmlSyntax matroska_track[] = {
> >> >> >> > { MATROSKA_ID_TRACKOPERATION, EBML_NEST, 0, offsetof(MatroskaTrack,operation), {.n=matroska_track_operation} },
> >> >> >> > { MATROSKA_ID_TRACKCONTENTENCODINGS,EBML_NEST, 0, 0, {.n=matroska_track_encodings} },
> >> >> >> > { MATROSKA_ID_TRACKMAXBLKADDID, EBML_UINT, 0, offsetof(MatroskaTrack,max_block_additional_id) },
> >> >> >> > + { MATROSKA_ID_CODECDELAY, EBML_UINT, 0, offsetof(MatroskaTrack,codec_delay) },
> >> >> >> > + { MATROSKA_ID_SEEKPREROLL, EBML_UINT, 0, offsetof(MatroskaTrack,seek_preroll) },
> >> >> >> > { MATROSKA_ID_TRACKFLAGENABLED, EBML_NONE },
> >> >> >> > { MATROSKA_ID_TRACKFLAGLACING, EBML_NONE },
> >> >> >> > { MATROSKA_ID_CODECNAME, EBML_NONE },
> >> >> >
> >> >> >> > @@ -1874,6 +1878,16 @@ static int matroska_read_header(AVFormatContext *s)
> >> >> >> > st->codec->bits_per_coded_sample = track->audio.bitdepth;
> >> >> >> > if (st->codec->codec_id != AV_CODEC_ID_AAC)
> >> >> >> > st->need_parsing = AVSTREAM_PARSE_HEADERS;
> >> >> >> > + if (track->codec_delay > 0) {
> >> >> >> > + st->skip_samples = av_rescale_q(track->codec_delay,
> >> >> >> > + (AVRational){1, 1000000000},
> >> >> >> > + (AVRational){1, st->codec->sample_rate});
> >> >> >> > + }
> >> >> >
> >> >> > i suspect this alone wont work when the user seeks back to the first
> >> >> > packet
> >> >>
> >> >> i don't understand why. can you please explain?
> >> >
> >> > because its set when parsing the header but when seeking back the
> >> > header is not re parsed so its not set again so the first packet
> >> > would then skip a different amount
> >> > thats unless iam missing something
> >> >
> >>
> >> yes, you are right. it is up to the decoder implementation to make sure
> >> that it uses the correct skip_samples value when the input timestamp is
> >> zero (or start of stream) when seeking.
> >
> > the decoder doesnt know when the timestamp is zero, a file might start
> > from a timestamp differnt than zero
> >
>
> i think i haven't communicated correctly about what i'm trying to
> achieve with this patch.
> basically, lavf will put this container value in the stream struct
> while parsing the
> header. once it populated, this field should not change (on seeking,
> etc.). so , it's a place
> where i can put the container field in the stream.
AVStream->skip_samples will simply cause side data to be added to the
next packet that indicate to the decoder that a specific number of
samples should be skiped. skip_samples will be reset to 0 after it
has been used in this way.
See the code in utils.c that uses skip_samples, its just 5 lines
A demuxer could just directly generate the sidedata but that is
probably often more complex implementation wise
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
No snowflake in an avalanche ever feels responsible. -- Voltaire
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