[FFmpeg-trac] #4362(ffmpeg:new): ffmpeg can't extract screenshot from webm if -loop 1 not included, fails silently

[FFmpeg]

#4362: ffmpeg can't extract screenshot from webm if -loop 1 not included, fails
silently
-----------------------------------+--------------------------------------
             Reporter:  copypaste  |                     Type:  defect
               Status:  new        |                 Priority:  normal
            Component:  ffmpeg     |                  Version:  git-master
             Keywords:             |               Blocked By:
             Blocking:             |  Reproduced by developer:  0
Analyzed by developer:  0          |
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 I own a site (8ch.net) where users are allowed to upload arbitrary WEBM
 (VP9/Opus or VP8/vorbis) and MP4 (H264/AAC only) files so long as they are
 under 8MB. Therefore, many users have come up with tricks and codec
 parameters to tune their files to try to get them to be under the limit.

 one-frame-webm-bug.webm ( uploaded to FTP, also available at
 https://media.8ch.net/test/src/1425957831333.webm ) was generated with the
 command:


 {{{
 ffmpeg -i shot0002.jpg -i happening.aac one-frame-webm-bug.webm
 }}}


 Browsers (Chrome and Firefox) understand this just fine. They display the
 image and then play the audio while leaving the image up for the entirety
 of the video. -loop 1 is not necessary and just a waste of filesize.

 However, my thumbnailing routine does this command (log attached):


 {{{
 ffmpeg -y -strict -2 -ss 10 -i one-frame-webm-bug.webm -an -vframes 1 -f
 mjpeg -vf scale=255:-1 test.jpg
 }}}


 ffmpeg fails because it's asking for frame 10 when only frame 0 was
 specified.

 Output file is empty, nothing was encoded (check -ss / -t / -frames
 parameters if used)

 What's even more annoying is it exits with 0 so I can't even detect there
 was an error and then run the command again with -ss 0.

 Please do not tell me "just use -loop 1", this is a user generated content
 site and as I said -loop 1 is a waste of filesize with no benefit because
 all players (even ffplay) understand it correctly, only ffmpeg doesn't.

 Please either change the exit status to something non-zero because this is
 obviously a failure or fix the underlying bug where it doesn't understand
 the video file correctly.

 Tested on versions 1.2.6, 2.5.4 and 2.6. Happens on all of them.

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Ticket URL: <https://trac.ffmpeg.org/ticket/4362>
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