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• How do I use ffmpeg with Python by passing File Objects (instead of locations to files on disk)

  1er mai 2012, par Lyle Pratt

  I'm trying to use ffmpeg with Python's subprocess module to convert some audio files. I grab the audio files from a URL and would like to just be able to pass the Python File Objects to ffmpeg, instead of first saving them to disk. It would also be very nice if I could just get back a file stream instead of having ffmpeg save the output to a file.

  For reference, this is what I'm doing now :

  tmp = "/dev/shm"
  
  audio_wav_file = requests.get(audio_url)
  
  ##              ##                         ##
  
  ## This is what I don't want to have to do ##
  
  wavfile = open(tmp+filename, 'wrb')   
  
  wavfile.write(audio_wav_file.content)
  
  wavfile.close()
  
  ##              ##                         ##
  
  conversion = subprocess.Popen('ffmpeg -i "'+tmp+filename+'" -y "'+tmp+filename_noext+'.flac" 2>&1', shell = True, stdout = subprocess.PIPE).stdout.read()

  Does anyone know how to do this ?

  Thanks !

• Does 'keyint infinite' improve overall compression with crf and mb-tree ?

  23 avril 2012, par HitomiTenshi

  After reading what intra-refresh does, I kinda got confused. I'm encoding for YouTube and YouTube will re-encode the video-file anyways, so I thought "why not removing all these heavy IDR-frames ?" I just want to compress my video as hard as possible, enabling everything that could help me getting a lower filesize, but still maintaining a high quality.

  I used to test around stuff with lossless QP encoding, but the only thing I could max out was the merange. Here is a paste of my x264 settings : Pastebin.

  I want to achieve highest compression while maintaining visually lossless quality. (using crf values around 10 - 13, and merange 32)

  Could anyone give me advice on how to compress my video super hard (without touching the crf value !). I also want to know if it's true, that keyint infinite reduces overall compression.

• Transcoding & displaying user-uploaded videos for cross-browser/platform compatibility

  5 avril 2012, par Jonathan Amend

  I want to display user-uploaded videos in high quality on different browsers/platforms. I think I have a pretty good start, but there are a few issues. I have at my disposal ffmpeg 0.10 (called from PHP) and jwPlayer 5.8 (licensed).

  Ideally I would like to support :

  • Browsers with Flash 9+
  • Modern Firefox/Chrome/Safari without Flash
  • iOS 4.1+
  • Android 2.2+

  My current transcoding commands are :

  $commands = array(
  
      'flv' => "/usr/bin/ffmpeg -y -i {$sourceFile} -b 500k -ar 22050 -ab 64 {$tmpFileName}.flv 2>&1",
  
      'webm' => "/usr/bin/ffmpeg -i {$sourceFile} -acodec libvorbis -ac 2 -ab 96k -ar 44100 -b 500k {$tmpFileName}.webm 2>&1",
  
      'mp4' => "/usr/bin/ffmpeg -i {$sourceFile} -acodec libfaac -ab 96k -vcodec libx264 -level 21 -refs 2 -vf 'scale=trunc(ih*a/2)*2:trunc(iw/a/2)*2' -b 500k -bt 1000k -threads 0 -f mp4 {$tmpFileName}.pre.mp4 2>&1",
  
      'jpg' => "/usr/bin/ffmpeg -y -i {$sourceFile} -ss 5 -vcodec mjpeg -vframes 1 -an -f rawvideo {$tmpFileName}.jpg 2>&1"
  
  );
  
  
  
  $fastStartCommand = "/usr/bin/qt-faststart {$tmpFileName}.pre.mp4 {$tmpFileName}.mp4");

  My current display code is this :

  <video controls="controls" width="{$width}" height="{$height}" poster="{$fileJPG}" style="width: {$width}px; height: {$height}px;">
  
      <source src="{$fileMP4}" type="video/mp4" data-ext="mp4"></source>
  
      <source src="{$fileWEBM}" type="video/webm" data-ext="webm"></source>
  
      <a href="http://stackoverflow.com/feeds/tag/{$fileMP4}" title="Play Video">
  
          <img border="0" src="http://stackoverflow.com/feeds/tag/{$fileJPG}" width='0' height='0' alt="Play Video" />
  
      </a>
  
  </video>
  
  <code class="echappe-js">&lt;script type=&quot;text/javascript&quot;&gt;<br />
  
  swfobject.embedSWF(<br />
  
      &amp;#39;/flash/jwPlayer.swf&amp;#39;,<br />
  
      &amp;#39;video&amp;#39;,<br />
  
      {$width},<br />
  
      {$height},<br />
  
      &amp;#39;9.0.0&amp;#39;,<br />
  
      &amp;#39;&amp;#39;,<br />
  
      {<br />
  
          file: &amp;#39;{$fileFLV}&amp;#39;,<br />
  
          width: {$width},<br />
  
          height: {$height},<br />
  
          provider: &amp;#39;video&amp;#39;,<br />
  
          stretching: &amp;#39;uniform&amp;#39;,<br />
  
          smoothing: &amp;#39;true&amp;#39;,<br />
  
          dock: &amp;#39;true&amp;#39;<br />
  
      },<br />
  
      {<br />
  
          menu: &amp;#39;false&amp;#39;,<br />
  
          allowfullscreen: &amp;#39;true&amp;#39;,<br />
  
          allowscriptaccess: &amp;#39;always&amp;#39;,<br />
  
          allownetworking: &amp;#39;always&amp;#39;,<br />
  
          wmode: &amp;#39;transparent&amp;#39;<br />
  
      }<br />
  
  );<br />
  
  &lt;/script&gt;
  
  

  The idea is to prefer the Flash player (we have many custom skins that we would like to keep using), then fall back to HTML 5 video, and if that fails, show the JPEG with a link to the mp4 file (that seems to work as a last-ditch effort for iOS 2/3 and old browsers so they can at least play the video by launching QuickTime).

  The main issues that I'm not sure how to solve right now are :

  • How can I show a higher quality video in Flash ? I tried using the mp4 video instead of the flv but it doesn't work and I only get sound, no video. I think Flash is supposed to support h.264 these days, but how ? And do I have to use a different transcoding method for older and newer versions of Flash ?
  • How can I transcode the video with better quality ? Right now I am using the same bitrate for all resolutions. Any chance there is a way for ffmpeg to adjust the bitrate automatically ? Or can I detect and match the resolution of the uploaded video to a list of resolution -> bitrates somehow ?