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• Capture raw video byte stream for real time transcoding

  9 septembre 2012, par user1145905

  I would like to achieve the following :

  Set up a proxy server to handle video requests by clients (for now, say all video requests from any Android video client) from a remote video server like YouTube, Vimeo, etc. I don't have access to the video files being requested, hence the need for a proxy server. I have settled for Squid. This proxy should process the video signal/stream being passed from the remote server before relaying it back to the requesting client.

  To achieve the above, I would either

  1. Need to figure out the precise location (URL) of the video resource being requested, download it really fast, and modify it as I want before HTTP streaming it back to the client as the transcoding continues (simultaneously, with some latency)

  2. Access the raw byte stream, pipe it into a transcoder (I'm thinking ffmpeg) and proceed with the streaming to client (also with some expected latency).

  Option #2 seems tricky to do but lends more flexibility to the kind of transcoding I would like to perform. I would have to actually handle raw data/packets, but I don't know if ffmpeg takes such input.

  In short, I'm looking for a solution to implement real-time transcoding of videos that I do not have direct access to from my proxy. Any suggestions on the tools or approaches I could use ? I have also read about Gstreamer (but could not tell if it's applicable to my situation), and MPlayer/MEncoder.

  And finally, a rather specific question : Are there any tools out there that, given a YouTube video URL, can download the byte stream for further processing ? That is, something similar to the Chrome YouTube downloader but one that can be integrated with a server-side script ?

  Thanks for any pointers/suggestions !

• ffmpeg time unit explanation and av_seek_frame method

  3 septembre 2013, par user325320

  What does time_base mean in ffmpeg ? document(here) says it is "frames per second".
  and I see in a real example that :

  AVFormatContext->streams[video_index]->time_base == 1 / 30000

  But video's AVCodecContext->time_base == 1001 / 60000

  This makes me quite confused, and I don't understand them.

  The second question is about av_seek_frame method.
  If seeking via time stamp (last parameter is AVSEEK_FLAG_BACKWARD or 0),
  the seek is started from current position read by av_seek_frame ?
  or from the start of the file ? or from the start position of decoding after last av_seek_frame call ?

• FFMPEG real-time buffer full frame dropped

  27 janvier 2015, par Burgaz

  I’m using FFMPEG on windows with direct show.
  I’m streaming RTMP (command below) and i need very low latency.
  Once run I get the following errors : [dshow @ 024ce800] real-time buffer 204% full ! frame dropped !

  ffmpeg -threads 6 -f dshow -i video=UScreenCapture -s 1920x1080 -an -vco
  dec libx264 -x264opts keyint=25:min-keyint=20 -b:v 1024k -preset ultrafast -tune zerolatency -crf 22 -r 10 -pix_fmt yuv420p -f flv rtmp ://server...

  Do you have an idea how to handle this kind of error ?

  Thanks
  Ronen