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

[Ulrik Mikaelsson <ulrik.mikaelsson@gmail.com>]

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 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
index 05c13228bc..c8c3b298ab 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((mp3->frames * 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);
-- 
2.39.2

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