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• Why low qmax value improve video quality ?

  14 novembre 2013, par theateist

  Maybe my questions doesn't make sense due to not understanding but please explain me what I miss because I did read posts and wiki and still it's not clear to me.

  As I understand setting low value for qmax will improve the quality by increasing the bitrate.
  Maybe I didn't understood something but isn't lowing the Q(quantization) will decrease the quantization levels and thus the bitrate which means degradation in quality ? Or in ffmpeg lowing Q means increasing the quantization levels ? If the last is true so it make sense that lower qmax improves the quality.

  If the above is true, so increasing qmax will decrease the quantization levels which means less bits for coding a quantization level. So, if number of bits for a level is lower, so total bits per frame will be lower, so how the encoder manage to get to the desired bitrate ?

• FFmpeg : AAC muxing into two different files in the same loop : The 2nd file is corrupted [on hold]

  1er septembre 2013, par user2677612

  We are using FFmpeg libraries git-ee94362 libavformat v55.2.100.
  Our purpose is to mux synthetic video and audio-file audio to 2 different files (in the same loop)
  with the the same format and parameters.

  With MP3 input, both M3U8 outputs are OK :

  Output file #0 : Total number of frames is : video = 229, audio = 347.

  Output file #1 : Total number of frames is : video = 229, audio = 347.

  But with AAC input, the 1st M3U8 output is OK, whereas the 2nd one - is not :

  Output file #0 : Total number of frames is : video = 403, audio = 690.

  Output file #1 : Total number of frames is : video = 3, audio = 690.

  It is exactly the same code in the main loop. We do not use the "aac_adtstoasc" filter in case of M3U output.
  By the way, the problem exist both with and without the filter,
  since in case of MP4 output, the 1st output file is OK, whereas the 2nd one - is not, - as well.

  Moreover :

  1) I have implemented the main loop as Windows threads, separated for every output file.

  2) I have separated input files, as well (i.e. use two identical input files).
  The problem remains !

  It seems that video PTS begins to be corrupted (wrong-calculated) for the 2nd (3rd, etc.) output file.

  If somebody is known about such a problem ? If yes, what can be a solution/workaround ?
  Thank you.

• Streaming video from nodejs to an open player

  27 août 2013, par Matthew Young

  Odd ball question for somebody just getting started with html5 players and streaming video....

  When using YouTube long videos can be scrolled towards then end then played from there. Assuming YouTube first pulls down metadata like total video start/stop points and a bunch of thumbnails for scrolling.

  Is this possible with an open html5 video player (like projekkter) ? Reason asking is that I have video data inside a mongo database that I would like to stream similar to the YouTube player.

  Inside mongo I have a bunch of smaller h264 files each in a document : actual raw h264 usually 1000kb (max 2 seconds), creation timestamp (long), and potentially a converted format (like mp4) for known clients. Idea is to query off a time range and order by creation time then piping the results into readable stream. There is a nice ffmpeg module to take streams and reformat if needed. Thought about piping the stream to the client with binaryjs and appending it into the player.

  But the source directives in the documentation are usually URLs plus I need to lock down the start/stop point for the total video being played plus thumbnails.