Recherche avancée

Sur d’autres sites (8656)

• How to find the actual size occupied by an AVFrame ?

  23 septembre 2013, par jsp99

  The main task at hand is to find the actual size of a decoded AVFrame.

  Here is some background information about the problem -
  I wrote a program which takes as input a media file and displays all the video frames of the file, on the screen. My Code (written in C using SDL and ffmpeg) worked perfectly with .wmv files. When it came to .mkv files, it failed (SIGSEGV) due to the following reason :

  Example : Suppose I have a decoded frame from my video stream of file (filename.mkv) in AVFrame *pFrame. The frame has a pix_fmt (pFrame->pix_fmt) of yuv420p. It has dimensions 640 * 346. The Y-plane has it's linesize (pFrame->linesize[0]) as 672.

  I think you get the point here. When I use avpicture_get_size() to get the size of the frame, it calculates a wrong size. It takes pix_fmt, width and height as arguments. Nowhere does it consider 672 instead of 640.

  avpicture_get_size() : Calculates the size in bytes that a picture of the given width and height would occupy if stored in the given picture format.

  I got around this problem by adding some yuv420p frame specific code, which can find the size of the frame in situations like above.

  • Can someone explain why are most of the decoded frames (from video streams of most of the formats) this way ? And why is it not this way with the wmv format ?

  But if I have to find the actual size occupied by an AVFrame of another format (Eg: yuv410p), I have to write the format specific code again. Coming to the main problem,

  • How can I find the actual size occupied the decoded AVFrame (size in bytes occupied by the data of the AVFrame) ?

  • I tried using av_image_get_buffer_size(), but I couldn't understand how to use the align parameter. Can someone explain the usage of the parameter align ? Tried using many other functions in pixdesc.c, but I am missing something.

• Find out what device to use for capturing with ffmpeg ?

  14 septembre 2013, par wvxvw

  I'm trying to broadcast my screen and I cannot capture audio. There's one complication however. I don't have pulseaudio, and it simply doesn't work on my system, so installing it is out of question. Below is the command I'm trying :

  ffmpeg -f alsa -i ??? -f x11grab -s 1920x1200 -r 15 -i :0.0 \
  
      -acodec pcm_s16le -vcodec libx264 \
  
      -preset fast -pix_fmt yuv420p -s 1280x800 -threads 0 -f flv "$URL"

  Here's the list of my audio devices :

  $ aplay -L
  
  null
  
      Discard all samples (playback) or generate zero samples (capture)
  
  default:CARD=PCH
  
      HDA Intel PCH, ALC269VB Analog
  
      Default Audio Device
  
  sysdefault:CARD=PCH
  
      HDA Intel PCH, ALC269VB Analog
  
      Default Audio Device
  
  front:CARD=PCH,DEV=0
  
      HDA Intel PCH, ALC269VB Analog
  
      Front speakers
  
  surround40:CARD=PCH,DEV=0
  
      HDA Intel PCH, ALC269VB Analog
  
      4.0 Surround output to Front and Rear speakers
  
  surround41:CARD=PCH,DEV=0
  
      HDA Intel PCH, ALC269VB Analog
  
      4.1 Surround output to Front, Rear and Subwoofer speakers
  
  surround50:CARD=PCH,DEV=0
  
      HDA Intel PCH, ALC269VB Analog
  
      5.0 Surround output to Front, Center and Rear speakers
  
  surround51:CARD=PCH,DEV=0
  
      HDA Intel PCH, ALC269VB Analog
  
      5.1 Surround output to Front, Center, Rear and Subwoofer speakers
  
  surround71:CARD=PCH,DEV=0
  
      HDA Intel PCH, ALC269VB Analog
  
      7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
  
  iec958:CARD=PCH,DEV=0
  
      HDA Intel PCH, ALC269VB Digital
  
      IEC958 (S/PDIF) Digital Audio Output
  
  hdmi:CARD=NVidia,DEV=0
  
      HDA NVidia, HDMI 0
  
      HDMI Audio Output
  
  hdmi:CARD=NVidia,DEV=1
  
      HDA NVidia, HDMI 0
  
      HDMI Audio Output
  
  hdmi:CARD=NVidia,DEV=2
  
      HDA NVidia, HDMI 0
  
      HDMI Audio Output
  
  hdmi:CARD=NVidia,DEV=3
  
      HDA NVidia, HDMI 0
  
      HDMI Audio Output

  I know that ??? should be something like hw:X,Y, but maybe it can be something else. I can't find the corresponding entry in the man page.

  As an aside, it would be great if you can suggest another audio codec. I can't find what are the options, and this particular one isn't compatible with FLV because of too high bitrate.

  PS. This is the error I'm getting :

  Could not write header for output file #0 (incorrect codec parameters ?): Invalid data found when processing input

• How do I run the qt ffmpeg wrapper example ? (error : cannot find -lavutil)

  29 août 2013, par James

  I am using QT 4.8 on the raspberry pi trying to save a binary stream to a video file like mp4. I was able to create and save static images by converting it into a QImage, but QT does not seem to support actually saving that stream (or the series of QImages) to a video file.

  The only option I may have found is qt ffmpeg Wrapper
  https://code.google.com/p/qtffmpegwrapper/

  but the example won't run out of the box. I am having the same exact problem as this guy :

  https://code.google.com/p/qtffmpegwrapper/issues/detail?id=14&colspec=ID%20Type%20Status%20Priority%20Milestone%20Owner%20Summary%20Opened%20Closed%20Modified#makechanges

  All I did was download it and try to run the included example, but no go.
  Am I supposed to download ffmpeg files prior to using this ? apt-get install ffmpeg ?

  Thanks !