使用ffmpeg从视频中提取帧-标头问题？

Question

I want to convert .AVI files coming from a camera-trap to individuals frames, ideally using ffmpeg. Up to now I am not succeeding.

The most simple thing I tried, to try to locate the problem, is this (I want all frames and my test file is test.avi):

ffmpeg -i test.avi output_%04d.png

It fails with the following console message:

[avi @ 0x559fb596f8c0] unknown stream type 73647578
[avi @ 0x559fb596f8c0] Something went wrong during header parsing, tag [0][0]id has size 338702712, I will ignore it and try to continue anyway.
[mjpeg @ 0x559fb59709e0] No JPEG data found in image
    Last message repeated 100 times
[avi @ 0x559fb596f8c0] decoding for stream 0 failed
[avi @ 0x559fb596f8c0] Could not find codec parameters for stream 0 (Video: mjpeg (MJPG / 0x47504A4D), none(bt470bg/unknown/unknown), 1280x720): unspecified pixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
[avi @ 0x559fb596f8c0] Could not find codec parameters for stream 1 (Video: none (JUNK / 0x4B4E554A), none, 11025x22050): unknown codec
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, avi, from 'test.avi':
  Duration: 00:00:10.50, start: 0.000000, bitrate: 28129 kb/s
    Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), none(bt470bg/unknown/unknown), 1280x720, 20.01 fps, 20.01 tbr, 20.01 tbn, 20.01 tbc
    Stream #0:1: Video: none (JUNK / 0x4B4E554A), none, 11025x22050, 11025 tbr, 11025 tbn, 11025 tbc
Stream mapping:
  Stream #0:1 -> #0:0 (? (?) -> png (native))
Decoder (codec none) not found for input stream #0:1

The actual video duration is 10s (when read using vlc for instance, and this is indeed the length of video programmed on the camera-trap. ffmpeg says the duration is 10.50s, and says there is a problem with header parsing (see above).

I have no idea how to sort this, despite having looked at more than many ffmpeg 'convert video to frames' post. Any hint would be appreciated, thanks.

Answer 1

If you look at the error message, you will see that the file has 2 video streams.

Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), none(bt470bg/unknown/unknown), 1280x720, 20.01 fps, 20.01 tbr, 20.01 tbn, 20.01 tbc
Stream #0:1: Video: none (JUNK / 0x4B4E554A), none, 11025x22050, 11025 tbr, 11025 tbn, 11025 tbc

and ffmpeg is trying to read for the second one:

Stream mapping:
  Stream #0:1 -> #0:0 (? (?) -> png (native))

You can use -map 0:0 to select the first stream.