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

[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=15.490612|dts=2186
 
 packet|codec_type=audio|stream_index=0|pts=218972160|pts_time=15.516735|dts=218972160|dts_time=15.516735|duration=368640|duration_time=0.026122|size=418|pos=249718|flags=K__|data_hash=CRC32:3789f3cf|side_data|side_data_type=Skip Samples|skip_samples=0|discard_padding=1152|skip_reason=0|discard_reason=0
 
-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_padding=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=15.542857|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|disposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposition:hearing_impaired=0|disposition:visual_impaired=0|disposition:clean_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails=0|disposition:captions=0|disposition:descriptions=0|disposition:metadata=0|disposition:dependent=0|disposition:still_image=0|tag:encoder=LAME3.93 
-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|probe_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_padding=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=218521600|duration=15.484807|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|disposition:lyrics=0|disposition:karaoke=0|disposition:forced=0|disposition:hearing_impaired=0|disposition:visual_impaired=0|disposition:clean_effects=0|disposition:attached_pic=0|disposition:timed_thumbnails=0|disposition:captions=0|disposition:descriptions=0|disposition:metadata=0|disposition:dependent=0|disposition:still_image=0|tag:encoder=LAME3.93
+format|filename=gapless.mp3|nb_streams=1|nb_programs=0|format_name=mp3|start_time=0.025057|duration=15.484807|size=250264|bit_rate=129295|probe_score=51|tag:title=test
-- 
2.39.2