Negative segment durations in m3u8 file

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Negative segment durations in m3u8 file

Valentin Schweitzer
Hi,

when using the HLS muxer, some segment durations in the
output m3u8 file are negative when specifying a very
short hls_time.

Using the attached 264 file and FFmpeg head,
this behavior can be recreated like this:

./ffmpeg -report -i test.264 -pix_fmt yuv420p -vcodec libx264 -b:v 10000k -hls_segment_type fmp4 -hls_time 0.1 -hls_flags split_by_time+second_level_segment_index -strftime 1 -hls_segment_filename stream-%%18d.m4s -hls_playlist_type event index.m3u8

The command line output can be found in the attached log file.
This command produces output along the lines of

[...]
#EXTINF:0.160000,
stream-000000000000000108.m4s
#EXTINF:-0.080000,
stream-000000000000000109.m4s
#EXTINF:0.200000,
stream-000000000000000110.m4s
#EXTINF:0.160000,
stream-000000000000000111.m4s
#EXTINF:-0.040000,
stream-000000000000000112.m4s
#EXTINF:0.200000,
[...]

An uncut example m3u8 file is attached.
The varying output lengths are expected, due to
splitting along I-Frames, although negative
durations seems like an error.

As I am not sure if this is a case of user
error, I'd like to ask for any advice
to fix this issue and, if possible, find
out why it occurs before opening a trac
ticket.

The command above is a shortened version
of the original command with which this
bug was discovered. A change of framerate
using -r 30 changes the output values,
but still leaves some negative timestamps.

This behaviour was tested on Ubuntu with
FFmpeg HEAD and on Windows with the latest
Zeranoe pre-built.

I would be thankful for any advice.
Greetings,
Valentin

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test.264 (814K) Download Attachment
ffmpeg-20200811-152051.log (170K) Download Attachment
index.m3u8 (7K) Download Attachment