[FFmpeg-devel] [PATCH] matroska: Set CodecDelay and SeekPreroll in the AVStream

[Vignesh Venkatasubramanian]

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.

> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Those who are best at talking, realize last or never when they are wrong.
>
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