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• Alter YUV values of AVFrames in FFMpeg

  1er février 2012, par Kage

  I'm trying to apply an effect to a video by altering the YUV values using FFMpeg programmatically in C.

  Let's say I want to increase the luminescence of each pixel of each frame by 100.

  I tried just altering the first frame of a video stream. I decoded the frame, added 100 to each Y value in the AVFrame->data[0], encoded the frame again and saved it into the video.

  However when I play the video back, it is not only the first frame that has been altered, but the first 30 frames.

  Why are the other frames effected when I only change the AVFrame->data of the first frame ?

  I tried again by changing all the Y, U and V values in AVFrame->data to 0 for only the first frame.

  When I play back the video, it starts off completely green like expected, after the first frame the video stays green for 30 frames. I can see the other frames start to come slowly through the green for 30 frames and then suddenly the green disappears and the video plays as normal. Why is it not just the first frame that is green ?

  My method is as follows :

  Video Stream

   |
  
   |     *(Get a frame)*
  
   |
  
   v

  AVPacket (encoded data)

   |
  
   |     *(Decode the frame)*
  
   |
  
   v

  AVFrame (raw data) --------------------------------------------------> AVFrame (raw data)

                    *(Edit AVFrame->data values)*
  
  
  
                                                         |
  
                                                         |     *(encode frame)*
  
                                                         |
  
                                                         V
  
                                                AVPacket (encoded data)
  
  
  
                                                         |
  
                                                         |     *(save frame)*
  
                                                         |
  
                                                         V
  
                                                    Video Stream

  Am I doing something obviously wrong ?

  How can I change just one frame without effecting the others ?

• Should I use the MP3 or AAC codec for a .mp4 file ?

  8 novembre 2014, par Justin Jenkins

  We have an encoding process in place using ffmpeg on Mac OS X. This process will take a source video and a couple files from that : .m3u8 video, .mp4 video and .mp3 audio file.

  By default we’ve used the video from our m3u8 process which is a h264 (via libx264) video with AAC (via libfaac) audio.

  We are mostly using these videos on mobile devices (hence the m3u8 files) but we also use the .mp4 files for Android, Windows Phone, etc. More and more we also need to offer these same videos on the web via either a flash player or HTML5 player.

  Therefore, we’d like to have the best audio/video codec combo for all these uses ... where I’m confused is to what is "standard" for a .mp4 file ?

  If the .mp4 uses the mp3 codec then it plays just fine everywhere but QuickTime, in QuickTime the video plays but there is not audio (works just fine in VLC player tho.)

  I’ve been told it’s due to how QuickTime uses file extensions to assume information about the video instead of trying to actually get the codec data from the file ? This does make some sense, if we encode the same file but use AAC for the audio codec then it works just fine in QuickTime.

  So --- what’s the "correct" or "ideal" audio/video codec combo --- is it best and safe to use AAC (i.e. will it work on a broad range of devices) even though it’s not a "free" codec ?

• Full HD video converted to FLV, slow playback in browser

  12 février 2012, par Boyan Georgiev

  I rendered a full HD video using Adobe AfterEffects CS5 in mp4 format. It plays just fine. I've got this video app to which I fed the mp4 file. The video app converts the mp4 to flv format and makes the video available via a web page. I've downloaded the resulting flv file to my local PC - it plays just fine in my VLC player. But, the problem is I'm getting awful playback inside my browser.

  I've made sure the issue is not bandwidth related.
  Both original mp4 file, and ffmpeg-converted FLV file, play perfectly using VLC player.
  I've tested the FLV file with two players - Agryia FLV Player Elite and JW Player. Both players play the video awfully - really slow and very choppy.

  Here's my ffmpeg -i myflvfile.flv :
  `

  Seems stream 0 codec frame rate differs from container frame rate: 119.88 (120000/1001) -> 59.92 (719/12)
  
  Input #0, flv, from '94044631305552037.flv':
  
  Metadata:
  
  duration        : 146
  
  width           : 1920
  
  height          : 1080
  
  videodatarate   : 684
  
  framerate       : 60
  
  videocodecid    : 7
  
  audiodatarate   : 62
  
  audiosamplerate : 22050
  
  audiosamplesize : 16
  
  stereo          : true
  
  audiocodecid    : 2
  
  major_brand     : mp42
  
  minor_version   : 0
  
  compatible_brands: mp42mp41
  
  creation_time   : 2012-02-10 00:55:19
  
  encoder         : Lavf52.111.0
  
  filesize        : 61969316
  
  Duration: 00:02:25.77, start: 0.034000, bitrate: 764 kb/s
  
  Stream #0.0: Video: h264 (High), yuv420p, 1920x1080 [PAR 3:4 DAR 4:3], 700 kb/s, 59.92 tbr, 1k tbn, 119.88 tbc
  
  Stream #0.1: Audio: mp3, 22050 Hz, stereo, s16, 64 kb/s`

  Can any one point me in the right direction here ? Why is playback perfect with VLC player of both the mp4 and the flv file on my local PC, yet in my browser, using two different players, the playback is so bad ?

  PS Here's my convert command :

  ffmpeg -y -i /var/www/sandverlag.com/htdocs/rmtk/videos/originals/94044631305552038.mp4 -vcodec libx264 -ar 22050 -ac 2 -vb 700000 -s 1920x1080 -crf 22 -threads 0 -f flv /var/www/sandverlag.com/htdocs/rmtk/videos/converted/94044631305552038.flv > /dev/null &