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• ffmpeg converting video to images while video file is being written

  15 octobre 2015, par user3398227

  Hopefully an easy question for an ffmpeg expert !

  I’m currently converting large (+6GB) mpeg video into an image sequence - which is working well using the below ffmpeg command :

  ffmpeg -i "input.mpeg" -vf - fps=fps=2 -f image2 -qscale 1 -s 1026x768 "output%6d.jpg"

  however i have to wait for the file to finish being written to disk before i kick off ffmpeg - but this takes a good hour or so to finish writing, but what i’ve noticed is that ffmpeg can start reading the file while its being written to disk - the only snag here is it gets to the end of the file and stops before the file has finished being written...

  Question is, is there a way that ffmpeg can convert to an image sequence at the same pace the video is being written (and not exit out ?)... or know to wait for the next frame to be written from the source. (unfortunately the input doesn’t support streaming, I only get a network drive and file to work off.. ) I thought i read somewhere that ffmpeg can process at the video frame rate but cant seem to find this command for love or money in the doco !!

  Thanks !

• Video codec not supported error when adding audio to mp4

  18 février 2019, par WPMed

  I work on an application which you can use to make still photos move. It’s basically a png sequence to mp4 converter.
  Recently we introduced a feature where users can add sound effects to the video.
  Since we released this feature, some users experience problems with the exported video. When they save the file and try to play it, they get a "Video codec not supported" error message. All they get is a black screen, and the audio playing in the background. I use FFmpeg to add audio (in mp3 format) to the mp4 video.
  Here’s an example video, which plays fine on my Mac and on my Samsung Galaxy S6 and S8, but buggy on Samsung SM-A310F (Android 7.0). This is how it looks like on the device.
  I tried to re-encode this video with all the FFmpeg commands I could find, but none of them seemed to work. Can someone spot something that’s not compatible with Android by analyzing the video I linked ?

• Changing video encoding quality : Raspberry pi+v4l2 (ffmpeg or direct v4l2 API)

  24 octobre 2023, par Bill Shubert

  We are using a raspberry pi 4 to acquire video. Using the x264 library for software encoding, we were able to select a usable quality level (generally in the 16-20 range), but the compression speed was much too slow to keep up with the video feed. We switched to ffmpeg's v4l2 hardware encoder, and it's plenty fast enough to keep up with the incoming video, but now the output is poor quality, too low to be usable for our application. We have tried the ffmpeg -crf flag from 20 all the way down to 5, and it seems to have little or no effect on the video quality. I dug through the ffmpeg source code and can't find any references to "crf", "quality", or even compression rate in the v4l2 codec of ffmpeg.

  


  Is there a way to change the quality level of your encoded video using the PI's v4l2 hardware video encoder ? If so, does ffmpeg support it in some way ? Hopefully I just missed how to pass it in. If raspi+video4linux does support selecting output quality, but ffmpeg doesn't use it, then I could either patch ffmpeg or write my own code to drive v4l2, but it's not a simple API to use so I'd rather stay with ffmpeg if I can.