Opened 5 years ago

Last modified 5 years ago

#2491 new enhancement

audio stream start_time & duration overspan when encoding & split a video (-ss, -t)

Reported by: ronny1982 Owned by:
Priority: minor Component: ffmpeg
Version: git-master Keywords:
Cc: Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no

Description

I'm trying to extract and encode a segment of a video with a given start time and duration.

Until version 0.10.7 the start time and duration of the extracted audio stream were almost accurate compared to the video stream.

Since version 0.11.3 additional audio packets are appended that lies outside of the requested duration -> the audio stream is 'much' longer than the video stream compared to the result with version 0.10.7.

Since version 1.1.4 the behavior changed again, the audio packets no longer starts with pts_time 0.0, instead they got an offset. This offset will also be added to the regular duration of the last audio packet. Technically the values belongs to the requested timespan:
first_packet_pts_time + packet_duration > -ss <start_time>
last packet_pts_time < -ss <start_time> + -t <duration>
However the output of version 0.10.7 is more logical...

Why making a fuss about 20~50ms additional difference between the stream durations? The higher accuracy (like in version 0.10.7) is required when you want to concatenate multiple segments, where different stream start times & durations playing an important role to prevent 'gaps' in the video stream (-> explained here)


shell script for testing:

#!/bin/sh

cd "$(dirname "$0")"

# extract and encode segments with different ffmpeg versions
ffmpeg-0.10.7 -i "Agnis Philosophy.mp4" -strict experimental -f mp4 -c:a aac -c:v mpeg4 -ss 00:00:11.000 -t 00:00:12.666 -y "agnis-part_0.10.7.mp4"
ffmpeg-0.11.3 -i "Agnis Philosophy.mp4" -strict experimental -f mp4 -c:a aac -c:v mpeg4 -ss 00:00:11.000 -t 00:00:12.666 -y "agnis-part_0.11.3.mp4"
ffmpeg-1.0.6 -i "Agnis Philosophy.mp4" -strict experimental -f mp4 -c:a aac -c:v mpeg4 -ss 00:00:11.000 -t 00:00:12.666 -y "agnis-part_1.0.6.mp4"
ffmpeg-1.1.4 -i "Agnis Philosophy.mp4" -strict experimental -f mp4 -c:a aac -c:v mpeg4 -ss 00:00:11.000 -t 00:00:12.666 -y "agnis-part_1.1.4.mp4"
ffmpeg-1.2 -i "Agnis Philosophy.mp4" -strict experimental -f mp4 -c:a aac -c:v mpeg4 -ss 00:00:11.000 -t 00:00:12.666 -y "agnis-part_1.2.mp4"

# extract stream infos from each encoded segment
ffprobe -show_streams 'agnis-part_0.10.7.mp4' | grep 'STREAM\|start_time\|duration\|nb_frames' > 'info_0.10.7.txt'
ffprobe -show_streams 'agnis-part_0.11.3.mp4' | grep 'STREAM\|start_time\|duration\|nb_frames' > 'info_0.11.3.txt'
ffprobe -show_streams 'agnis-part_1.0.6.mp4' | grep 'STREAM\|start_time\|duration\|nb_frames' > 'info_1.0.6.txt'
ffprobe -show_streams 'agnis-part_1.1.4.mp4' | grep 'STREAM\|start_time\|duration\|nb_frames' > 'info_1.1.4.txt'
ffprobe -show_streams 'agnis-part_1.2.mp4' | grep 'STREAM\|start_time\|duration\|nb_frames' > 'info_1.2.txt'

# extract packet infos from each encoded segment
ffprobe -show_packets 'agnis-part_0.10.7.mp4' | grep 'PACKET\|codec_type\|pts_time\|dts_time\|duration_time' > 'packets_0.10.7.txt'
ffprobe -show_packets 'agnis-part_0.11.3.mp4' | grep 'PACKET\|codec_type\|pts_time\|dts_time\|duration_time' > 'packets_0.11.3.txt'
ffprobe -show_packets 'agnis-part_1.0.6.mp4' | grep 'PACKET\|codec_type\|pts_time\|dts_time\|duration_time' > 'packets_1.0.6.txt'
ffprobe -show_packets 'agnis-part_1.1.4.mp4' | grep 'PACKET\|codec_type\|pts_time\|dts_time\|duration_time' > 'packets_1.1.4.txt'
ffprobe -show_packets 'agnis-part_1.2.mp4' | grep 'PACKET\|codec_type\|pts_time\|dts_time\|duration_time' > 'packets_1.2.txt'

Taking a look into some selected stream infos of each encoded segment from ffprobe. You can notice the 'evolution' of the audio stream (first stream is video, second stream is audio):

ffmpeg-0.9.2 & ffmpeg-0.10.7 ffmpeg-0.11.3 & ffmpeg-1.0.6 fmpeg-1.1.4 & ffmpeg-1.2
[STREAM][STREAM][STREAM]
start_time=0.000000start_time=0.000000start_time=0.000000
duration=12.666667duration=12.666667duration=12.666667
nb_frames=380nb_frames=380nb_frames=380
[/STREAM][/STREAM][/STREAM]
[STREAM][STREAM][STREAM]
start_time=0.000000start_time=0.000000start_time=-0.016961
duration=12.678095duration=12.701315duration=12.701315
nb_frames=546nb_frames=547nb_frames=547
[/STREAM][/STREAM][/STREAM]

Source Video:

Results:

*not sure if this behavior is a defect or is wanted by the developers, so setting the ticket to: enhancement with minor priority

Change History (1)

comment:1 Changed 5 years ago by ronny1982

Additional Notes:

  • the timing difference depends on audio codec
  • when using audio copy all ffmpeg versions works like expected (only packets with timestamps in the requested timespan where copied)
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