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• ffmpeg capture for usb v4l2 card

  8 décembre 2020, par elbarna

  I have a Grabby Terratec USB card.

  


  Bus 001 Device 006: ID 0ccd:10af TerraTec Electronic GmbH Terratec G1


  


  With mencoder I capture fine video and audio using a script like this one

  


  #!/bin/sh
#script for capture
#settings for pal 25 fps 720:576 normid=5
#settings for ntsc 30000/1001 fps normid 0 720:480
#settings for INPUT,0=composite,1=s-video,but depend on card

TITLE="MYMOVIE"
CROP="612:467:16:1"
SCALE="560:432"
DEVVID=0
INPUT=1
ADEVICE=hw.2,0
NORMID=5
WIDTH=640
HEIGHT=480
FPS=25
AUDIORATE=48000
ASPECT=4/3
VFS="yadif,crop=$CROP,scale=$SCALE,harddup"

mencoder tv:// -tv driver=v4l2:normid=$NORMID:width=$WIDTH:height=$HEIGHT:device=/dev/video$DEVVID:input=$INPUT:fps=$FPS:alsa:adevice=$ADEVICE:audiorate=${AUDIORATE}:amode=1:forceaudio:immediatemode=0 -of mpeg -mpegopts format=dvd -oac lavc -ovc lavc -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=8000:vbitrate=6000:keyint=15:acodec=ac3:abitrate=320 -aspect $ASPECT -vf $VFS -o "$TITLE".mpg


  


  The script capture audio because this line is present

  


  :amode=1:forceaudio:immediatemode=0


  


  Now the problem, I want to capture using ffmpeg with libx265 and aac

  


  #!/bin/sh
SCALE=528:400
CROP=616:471:14:0
ASPECT=4:3
TITLE="MYTITLE"

#usbstream:CARD=Generic
#    HD-Audio Generic
#    USB Stream Output
#sysdefault:CARD=G1
#    Terratec G1, USB Audio
#    Default Audio Device
#front:CARD=G1,DEV=0
#    Terratec G1, USB Audio
#    Front output / input
#usbstream:CARD=G1
#    Terratec G1
#    USB Stream Output

ffmpeg -y -f video4linux2 -i /dev/video0  -thread_queue_size 512 -f alsa -i hw:CARD=G1 -ac 2 -vf yadif,crop=$CROP,scale=$SCALE -c:v libx265 -c:a aac -b:v 1200k -b:a 320k -metadata language=eng -metadata title="Mymovie" -aspect $ASPECT "$TITLE".mkv


  


  The problem is.. video is captured but without audio, I have tried the line

  


   -f alsa -i hw:CARD=G1


  


  and

  


   -f alsa -i hw:CARD=G1,DEV=0


  


  and

  


   -f alsa -i hw:2,0


  


  But no way. The option " :amode=1:forceaudio:immediatemode=0" doesn't exist on ffmpeg.
Any suggestion ?Thanks

  


• Audio/Video de-synchronisation when playing a video on Chrome

  30 novembre 2020, par Sonia Seddiki

  I've been recently working on a project where I try to play a "custom-made" video on an HTML5 player. By custom-made, I mean I concatenate a bunch of videos together using FFmpeg concat demuxer, each of them having the same properties (FPS, bitrate, resolution, timebase, etc).

  


  Now, I'm having a few issues regarding audio/video synchronisation, with a twist : it does not happen on every video player. The video is perfectly synchronised when read on Firefox, but not on Chrome. It is synchronised when read on a "local" video player like VLC.

  


  I assume it has to do with how the video data is presented to the player. I read a little about PTS, DTS, I-P-B frames and I guess the final output may be a little messed up ? But I don't really have a strong lead to follow here.

  


  I tried to find info on how the HTML5 player was implemented by both browsers, but couldn't find much (again, I'm probably not googling this right). Does anyone here know a bit more about the technical aspect of how a video is actually played in a browser ? Or any clue as to why this de-synchronisation doesn't happen on every platform ?

  


  Thank you so much for your help !

  


• Unexpected Exception when using ffmpeg.wasm in Chrome extension

  18 novembre 2020, par Javierd98

  I'm trying to implement a chrome extension which allows me to play flv videos by transcoding them to mp4 and then inserting a video player as it's done on the transcode example from ffmpeg.wasm.

  


  As chrome extensions don't support the execution of downloaded code, I need to use a downloaded version of ffmpeg-core.
I've downloaded the 0.8.4 version and included the folder on the manifest under web_accessible_resources, so that on the javascript file for trancoding the code is :

  


  const { createFFmpeg, fetchFile } = FFmpeg;
const ffmpeg = createFFmpeg({
  log: true,
  corePath: chrome.runtime.getURL('ffmpeg-core/ffmpeg-core.js'),
});

const transcode = async (file) => {
  const { name } = file;
  console.log('Loading ffmpeg-core.js. Transcode URL.');
  await ffmpeg.load();
  console.log('ffmpeg-core loaded.');

  let blob = await fetch(file).then(r => r.blob());
  console.log('blob downloaded');

  ffmpeg.FS('writeFile', name, blob);
  console.log('Start transcoding');
  await ffmpeg.run('-i', name,  'output.mp4');
  console.log('Complete transcoding');
  const data = ffmpeg.FS('readFile', 'output.mp4');

  const video = document.getElementById('output-video');
  video.src = URL.createObjectURL(new Blob([data.buffer], { type: 'video/mp4' }));
}


  


  Once the transcode function is executed, I get the following exception :

  


  ffmpeg.min.js:1 Uncaught (in promise) TypeError: t is not a function
    at ffmpeg.min.js:1
    at f (ffmpeg.min.js:1)
    at Generator._invoke (ffmpeg.min.js:1)
    at Generator.next (ffmpeg.min.js:1)
    at i (ffmpeg.min.js:1)
    at c (ffmpeg.min.js:1)


  


  

  


  Does somebody have any idea of why could this be happening ?

  


  Thanks a lot !