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

[Hendrik Leppkes]

On Tue, Oct 4, 2016 at 2:45 AM, 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;
>              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
> --

Presumably when these tests were setup, someone verified that their
output was sane and proper, and gapless.
So when these are changed, I have to ask - what exactly changes in
this output? The hashes unfortunately don't tell us that.

- Hendrik