[FFmpeg-devel] [PATCH v2] avformat/mp3dec: Subtract known padding from duration

[Tomas Härdin]

ons 2023-08-23 klockan 11:55 +0200 skrev Ulrik Mikaelsson:
> When an Info-tag is present, marking initial and trailing samples as
> padding, those samples should not be included in the calculation of
> track
> duration.
> 
> This solves a surprising user experience where converting a WAV->MP3-
> >WAV,
> ffprobe will show the duration of the mp3 as slightly longer than
> both the
> input and the output.
> ---
>  libavformat/mp3dec.c                 | 3 ++-
>  tests/ref/fate/gapless-mp3-side-data | 4 ++--
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
> index 05c13228bc..54947f521e 100644
> --- a/libavformat/mp3dec.c
> +++ b/libavformat/mp3dec.c
> @@ -350,7 +350,8 @@ static int mp3_parse_vbr_tags(AVFormatContext *s,
> AVStream *st, int64_t base)
>      avio_seek(s->pb, base + vbrtag_size, SEEK_SET);
>  
>      if (mp3->frames)
> -        st->duration = av_rescale_q(mp3->frames, (AVRational){spf,
> c.sample_rate},
> +        st->duration = av_rescale_q(((uint64_t)mp3->frames *
> (uint64_t)spf) - mp3->start_pad - mp3->end_pad,
> +                                    (AVRational){1, c.sample_rate},
>                                      st->time_base);
>      if (mp3->header_filesize && mp3->frames && !mp3->is_cbr)
>          st->codecpar->bit_rate = av_rescale(mp3->header_filesize, 8
> * c.sample_rate, mp3->frames * (int64_t)spf);
> diff --git a/tests/ref/fate/gapless-mp3-side-data
> b/tests/ref/fate/gapless-mp3-side-data
> index caf42068dc..495a5bb865 100644
> --- a/tests/ref/fate/gapless-mp3-side-data
> +++ b/tests/ref/fate/gapless-mp3-side-data
> @@ -596,5 +596,5 @@
> packet|codec_type=audio|stream_index=0|pts=218603520|pts_time=15.4906
> 12|dts=2186
>  
>  packet|codec_type=audio|stream_index=0|pts=218972160|pts_time=15.516
> 735|dts=218972160|dts_time=15.516735|duration=368640|duration_time=0.
> 026122|size=418|pos=249718|flags=K__|data_hash=CRC32:3789f3cf|side_da
> ta|side_data_type=Skip
> Samples|skip_samples=0|discard_padding=1152|skip_reason=0|discard_rea
> son=0
>  
> -
> stream|index=0|codec_name=mp3|profile=unknown|codec_type=audio|codec_t
> ag_string=[0][0][0][0]|codec_tag=0x0000|sample_fmt=fltp|sample_rate=4
> 4100|channels=2|channel_layout=stereo|bits_per_sample=0|initial_paddi
> ng=0|id=N/A|r_frame_rate=0/0|avg_frame_rate=0/0|time_base=1/14112000|
> start_pts=353600|start_time=0.025057|duration_ts=219340800|duration=1
> 5.542857|bit_rate=128000|max_bit_rate=N/A|bits_per_raw_sample=N/A|nb_
> frames=N/A|nb_read_frames=N/A|nb_read_packets=595|disposition:default
> =0|disposition:dub=0|disposition:original=0|disposition:comment=0|dis
> position:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposit
> ion:hearing_impaired=0|disposition:visual_impaired=0|disposition:clea
> n_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails=0
> |disposition:captions=0|disposition:descriptions=0|disposition:metada
> ta=0|disposition:dependent=0|disposition:still_image=0|tag:encoder=LA
> ME3.93 
> -
> format|filename=gapless.mp3|nb_streams=1|nb_programs=0|format_name=mp3
> |start_time=0.025057|duration=15.542857|size=250264|bit_rate=128812|p
> robe_score=51|tag:title=test
> +stream|index=0|codec_name=mp3|profile=unknown|codec_type=audio|codec
> _tag_string=[0][0][0][0]|codec_tag=0x0000|sample_fmt=fltp|sample_rate
> =44100|channels=2|channel_layout=stereo|bits_per_sample=0|initial_pad
> ding=0|id=N/A|r_frame_rate=0/0|avg_frame_rate=0/0|time_base=1/1411200
> 0|start_pts=353600|start_time=0.025057|duration_ts=218521600|duration
> =15.484807|bit_rate=128000|max_bit_rate=N/A|bits_per_raw_sample=N/A|n
> b_frames=N/A|nb_read_frames=N/A|nb_read_packets=595|disposition:defau
> lt=0|disposition:dub=0|disposition:original=0|disposition:comment=0|d
> isposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|dispos
> ition:hearing_impaired=0|disposition:visual_impaired=0|disposition:cl
> ean_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails
> =0|disposition:captions=0|disposition:descriptions=0|disposition:meta
> data=0|disposition:dependent=0|disposition:still_image=0|tag:encoder=
> LAME3.93
> +format|filename=gapless.mp3|nb_streams=1|nb_programs=0|format_name=m
> p3|start_time=0.025057|duration=15.484807|size=250264|bit_rate=129295
> |probe_score=51|tag:title=test

This still fails fate-seek-extra-mp3

/Tomas