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• How can I capture audio AND video simultenaous with ffmpeg from an USB capture device

  5 octobre 2011, par oban

  I'm capturing a video by means of an USB Terratec Grabster AV350 (which is based on the em2860 chip).

  I don't succeed to get the audio when it is played . If I play the captured video with vlc or with ffplay I got only 3 seconds sound and then a silence for the rest of the video ...

  During the capturing I don't get any errors. At the end it indicates the size of the video and audio captured ....

  I'm using the ffmpeg command for this :

  ffmpeg -f alsa -ac 2 -i hw:3 -f video4linux2 -i /dev/video0 -acodec ac3 -ab 128k -vcodec mpeg4 -b 6000k -r 25 test5.avi

  The log is :

  [alsa @ 0x9bcd420]Estimating duration from bitrate, this may be inaccurate
  Input #0, alsa, from 'hw:3' :
  Duration : N/A, start : 69930.998994, bitrate : N/A
  Stream #0.0 : Audio : pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
  [video4linux2 @ 0x9bf5d30]Estimating duration from bitrate, this may be inaccurate
  Input #1, video4linux2, from '/dev/video0' :
  Duration : N/A, start : 1307111377.654173, bitrate : -2147483 kb/s
  Stream #1.0 : Video : rawvideo, yuyv422, 720x576, -2147483 kb/s, 1000k tbr, 1000k tbn, 1000k tbc
  [ac3 @ 0x9bf9590]No channel layout specified. The encoder will guess the layout, but it might be incorrect.
  Output #0, avi, to 'test5.avi' :
  Metadata :
  ISFT : Lavf52.64.2
  Stream #0.0 : Video : mpeg4, yuv420p, 720x576, q=2-31, 6000 kb/s, 25 tbn, 25 tbc
  Stream #0.1 : Audio : ac3, 44100 Hz, stereo, s16, 128 kb/s
  Stream mapping :
  Stream #1.0 -> #0.0
  Stream #0.0 -> #0.1
  Press [q] to stop encoding
  frame= 1283 fps= 25 q=2.3 Lsize= 38677kB time=51.32 bitrate=6173.9kbits/s
  video:37755kB audio:846kB global headers:0kB muxing overhead 0.198922%

  If I reduce the command for only capturing audio, then the audio file can be played successfully :

  ffmpeg -f alsa -ac 2 -i hw:3,0 -acodec ac3 -ab 128k test5.avi

  [alsa @ 0x8ede420]Estimating duration from bitrate, this may be inaccurate
  Input #0, alsa, from 'hw:3,0' :
  Duration : N/A, start : 70395.998935, bitrate : N/A
  Stream #0.0 : Audio : pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
  [ac3 @ 0x8eebac0]No channel layout specified. The encoder will guess the layout, but it might be incorrect.
  Output #0, avi, to 'test5.avi' :
  Metadata :
  ISFT : Lavf52.64.2
  Stream #0.0 : Audio : ac3, 44100 Hz, stereo, s16, 128 kb/s
  Stream mapping :
  Stream #0.0 -> #0.0
  Press [q] to stop encoding
  size= 227kB time=13.62 bitrate= 136.8kbits/s
  video:0kB audio:213kB global headers:0kB muxing overhead 6.902375%

  If I run the command for only video capturing then vlc or ffplay can play the video successfully :

  ffmpeg -f video4linux2 -i /dev/video0 -vcodec mpeg4 -b 12000k -r 25 test5.avi

  [video4linux2 @ 0x91d6420]Estimating duration from bitrate, this may be inaccurate
  Input #0, video4linux2, from '/dev/video0' :
  Duration : N/A, start : 1307112044.025687, bitrate : -2147483 kb/s
  Stream #0.0 : Video : rawvideo, yuyv422, 720x576, -2147483 kb/s, 1000k tbr, 1000k tbn, 1000k tbc
  Output #0, avi, to 'test5.avi' :
  Metadata :
  ISFT : Lavf52.64.2
  Stream #0.0 : Video : mpeg4, yuv420p, 720x576, q=2-31, 12000 kb/s, 25 tbn, 25 tbc
  Stream mapping :
  Stream #0.0 -> #0.0
  Press [q] to stop encoding
  frame= 388 fps= 25 q=2.0 Lsize= 12963kB time=15.52 bitrate=6842.5kbits/s
  video:12949kB audio:0kB global headers:0kB muxing overhead 0.114584%

  Strange behaviour I noticed is that when I tried capturing video and audio, I can not capture the audio afterwards any more,
  unless I unplug the AV350 first.

  The G350 is located at card 3 :

  htpc@htpc-01 :/proc/asound/G350/pcm0c$ more info
  card : 3
  device : 0
  subdevice : 0
  stream : CAPTURE
  id : USB Audio
  name : USB Audio
  subname : subdevice #0
  class : 0
  subclass : 0
  subdevices_count : 1
  subdevices_avail : 1

  The OS is a Linux 2.6.38-8-generic with the Ubuntu Natty Narwhal version

  Any help on how to tackle this issue would be great ....

  Thanks !

• Separate mxf_essence_container_uls for audio and video.

  10 décembre 2011, par Carl Eugen Hoyos

  Separate mxf_essence_container_uls for audio and video.

• What is Video Lagrange factor and how to achieve Constant bit rate ?

  12 décembre 2011, par Tarun

  I want to perform transcoding using FFMPEG. My target is to acheive CBR i.e Constant bit rate. But even using option like -maxrate and -minrate I am unable to acheive it.
  I know when converting to x264 if I choose CBR, it will deteriorate the video quality but I am OK with it since I want to use it for streaming.

  Please help me asap