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FFMPEG output is black video, with audio

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Michael Gaynor
FFMPEG output is black video, with audio
on Nov 6, 2012 at 7:00:47 pm

Hi guys,
I installed ffmpeg on mac os x a couple weeks ago, and it was working great, then about a week ago, for no apparent reason, it began spitting out mp4's with no video, but with the correct duration and audio intact. I have since then tried multiple scripts in terminal, reinstalled ffmpeg, and even installed it on another machine to have the same results.
I know this is probably a user-error but I would really like to get this resolved! This is the most recent script in terminal that failed.

$ ffmpeg -i desktop/gm-outlook-v03.mov -c:v libx264 -crf 22 desktop/out.mp4

Also, this came up during the encode:

[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f99f981ae00] Stream #1: not enough frames to estimate rate; consider increasing probesize
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f99f981ae00] Stream #2: not enough frames to estimate rate; consider increasing probesize
Guessed Channel Layout for Input Stream #0.1 : stereo

But im not sure if that's relevant


Thanks for the help!


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Lou Logan
Re: FFMPEG output is black video, with audio
on Nov 10, 2012 at 8:54:46 pm

Please provide the complete ffmpeg console output. Without it I can only guess what the issue is, but I'm assuming that it is creating an output, which your player (QuickTime?) can not properly decode, due to the colorspace and/or subsampling of your input. FFmpeg, by default, will attempt to convert to the highest supported sampling mode by the encoder to avoid degradation of color information.

Try adding the following option as an output option:
-pix_fmt yuv420p


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Michael Gaynor
Re: FFMPEG output is black video, with audio
on Nov 13, 2012 at 8:37:24 pm

Wow that worked! What is that option changing in the video? Thanks so much!


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Lou Logan
Re: FFMPEG output is black video, with audio
on Nov 25, 2012 at 1:20:10 am

It is converting from one pixel format to another. The old default was to automatically convert everything to yuv420p, which is supported by all decoders. libx264 can now encode up to yuv444p (there is also libx264rgb), so the default behavior with your version of ffmpeg now attempts to use the highest supported pixel format that is inferred from your input. This is technically "good" but not always in practice; the result may not be supported by most decoders (except anything from FFmpeg of course), and you may or may not see artifacts, blurring, and or color loss due to chroma sub-sampling.


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