[FFmpeg-devel] [PATCH] matroska: Set CodecDelay and SeekPreroll in the AVStream
Vignesh Venkatasubramanian
vigneshv at google.com
Fri Oct 4 01:49:08 CEST 2013
On Thu, Sep 26, 2013 at 5:11 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> 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
>
Here is what I am trying to achieve: I need to use libavformat's
demuxer to demux the file but not use libavcodec for the decoding. So
in that case, i need libavformat to export this codec delay container
element's value somewhere. I presumed that to be the AVStream
structure. Can you please tell me how to do this if not through
AVStream?
The same goes for the other SeekPreRoll element too.
Thanks!
> [...]
> --
> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> No snowflake in an avalanche ever feels responsible. -- Voltaire
>
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