[FFmpeg-devel] [PATCH 3/3] lavf/mp3dec: read encoder delay/padding from Info tag

[Jon Toohill]

On Tue, Oct 4, 2016 at 7:19 AM, wm4 <nfxjfg at googlemail.com> wrote:

> On Mon,  3 Oct 2016 17:45:08 -0700
> Jon Toohill <jtoohill-at-google.com at ffmpeg.org> wrote:
>
> > Muxers can check AVCodecParameters.initial_padding for the
> > encoder+decoder delay, and read the AV_PKT_DATA_SKIP_SAMPLES
> > side data from the last packet for the encoder padding.
> >
> > This change also fixes the first_discard_sample calculation
> > which erroneously included the decoder delay. Decoder delay
> > is already accounted for in st->skip_samples. The affected
> > FATE tests have been updated accordingly.
> > ---
> >  libavformat/mp3dec.c                 |  3 ++-
> >  tests/ref/fate/audiomatch-square-mp3 |  2 +-
> >  tests/ref/fate/gapless-mp3           | 10 +++++-----
> >  3 files changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
> > index 56c7f8c..e8b2428 100644
> > --- a/libavformat/mp3dec.c
> > +++ b/libavformat/mp3dec.c
> > @@ -239,9 +239,10 @@ static void mp3_parse_info_tag(AVFormatContext *s,
> AVStream *st,
> >
> >          mp3->start_pad = v>>12;
> >          mp3->  end_pad = v&4095;
> > +        st->codecpar->initial_padding = mp3->start_pad + 528 + 1;
> >          st->start_skip_samples = mp3->start_pad + 528 + 1;
> >          if (mp3->frames) {
> > -            st->first_discard_sample = -mp3->end_pad + 528 + 1 +
> mp3->frames * (int64_t)spf;
> > +            st->first_discard_sample = -mp3->end_pad + mp3->frames *
> (int64_t)spf;
>
> How does mixing these even make sense?
>

mp3enc.c already uses initial_padding for the encoder delay, and as you
previously pointed out, mp3dec.c already uses AV_PKT_START_SKIP_SAMPLES for
the encoder delay. I'm not attempting to solve the inconsistency in this
patch set.


> >              st->last_discard_sample = mp3->frames * (int64_t)spf;
> >          }
> >          if (!st->start_time)
> > diff --git a/tests/ref/fate/audiomatch-square-mp3
> b/tests/ref/fate/audiomatch-square-mp3
> > index 8de55c2..05176a0 100644
> > --- a/tests/ref/fate/audiomatch-square-mp3
> > +++ b/tests/ref/fate/audiomatch-square-mp3
> > @@ -1 +1 @@
> > -presig: 0 postsig:0 c: 0.9447 lenerr:0
> > +presig: 0 postsig:-529 c: 0.9334 lenerr:-529
> > diff --git a/tests/ref/fate/gapless-mp3 b/tests/ref/fate/gapless-mp3
> > index ebe7bfa..8b80bfc 100644
> > --- a/tests/ref/fate/gapless-mp3
> > +++ b/tests/ref/fate/gapless-mp3
> > @@ -1,5 +1,5 @@
> > -37534a3bcc3ef306e8c5ebfcfedfc41c *tests/data/fate/gapless-mp3.out-1
> > -c96c3ae7bd3300fd2f4debac222de5b7
> > -0cd1cdbcfd5cdbf6270cd98219bf31cd *tests/data/fate/gapless-mp3.out-2
> > -c96c3ae7bd3300fd2f4debac222de5b7
> > -9d3d8ba8a61b534f2d02ee648d6a8229 *tests/data/fate/gapless-mp3.out-3
> > +81695be427d45e8be4d527a6b2af2a85 *tests/data/fate/gapless-mp3.out-1
> > +c7879a827ab017364774069268d9a267
> > +62d074296f8c84a5f86a6afdd7bab459 *tests/data/fate/gapless-mp3.out-2
> > +c7879a827ab017364774069268d9a267
> > +e931f3fe1ba25e0d5eece4977c4061a9 *tests/data/fate/gapless-mp3.out-3
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