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• My crazy linux.conf.au week

  9 février 2012, par silvia

  In January I attended the annual Australian Linux and Open Source conference (LCA). But since I was sick all of January and had a lot to catch up on, I never got around to sharing all the talks that I gave during that time.

  Drupal Down Under

  It started with a talk at Drupal Down Under, which happened the weekend before LCA. I gave a talk titled “HTML5 video specifications” (video, slides).

  I spoke about the video and audio element in HTML5, how to provide fallback content, how to encode content, how to control them from JavaScript, and briefly about Drupal video modules, though the next presentation provided much more insight into those. I explained how to make the HTML5 media elements accessible, including accessible controls, captions, audio descriptions, and the new WebVTT file format. I ran out of time to introduce the last section of my slides which are on WebRTC.

  Linux.conf.au

  On the first day of LCA I gave a talk both in the Multimedia Miniconf and the Browser Miniconf.

  Browser Miniconf

  In the Browser Miniconf I talked about “Web Standardisation – how browser vendors collaborate, or not” (slides). Maybe the most interesting part about this was that I tried out a new slide “deck” tool called impress.js. I’m not yet sure if I like it but it worked well for this talk, in which I explained how the HTML5 spec is authored and who has input.

  I also sat on a panel of browser developers in the Browser Miniconf (more as a standards than as a browser developer, but that’s close enough). We were asked about all kinds of latest developments in HTML5, CSS3, and media standards in the browser.

  Multimedia Miniconf

  In the Multimedia Miniconf I gave a “HTML5 media accessibility update” (slides). I talked about the accessibility problems of Flash, how native HTML5 video players will be better, about accessible video controls, captions, navigation chapters, audio descriptions, and WebVTT. I also provided a demo of how to synchronize multiple video elements using a polyfill for the multitrack API.

  I also provided an update on HTTP adaptive streaming APIs as a lightning talk in the Multimedia Miniconf. I used an extract of the Drupal conference slides for it.

  Main conference

  Finally, and most importantly, Alice Boxhall and myself gave a talk in the main linux.conf.au titled “Developing Accessible Web Apps – how hard can it be ?” (video, slides). I spoke about a process that you can follow to make your Web applications accessible. I’m writing a separate blog post to explain this in more detail. In her part, Alice dug below the surface of browsers to explain how the accessibility markup that Web developers provide is transformed into data structures that are handed to accessibility technologies.

• passing script variable of filename with spaces in bash to external program (ffmpeg) fails

  13 janvier 2016, par BostonScott

  Short story : I’m trying to write a script that will use FFmpeg to convert the many files stored in one directory to a "standard" mp4 format and save the converted files in another directory. It’s been a learning experience (a fun one !) since I haven’t done any real coding since using Pascal and FORTRAN on an IBM 370 mainframe was in vogue.

  Essentially the script takes the filename, strips the path and extension off it, reassembles the filename with the path and an mp4 extension and calls FFmpeg with some set parameters to do the conversion. If the directory contains only video files with without spaces in the names, then everything works fine. If the filenames contain spaces, then FFmpeg is not able to process the file and moves on to the next one. The error indicates that FFMpeg is only seeing the filename up to the first space. I’ve included both the script and output below.

  Thanks for any help and suggestions you may have. If you think I should be doing this in another way, please by all means, give me your suggestions. As I said, it’s been a long time since I did anything like this. I’m enjoying it though.

  I’ve include the code first followed by example output.

  for file in ./TBC/*.mp4
  
      do
  
  
  
      echo "Start of iteration"
  
      echo "Full text of file name:" $file
  
  
  
      #Remove everything up to  "C/" (filename without path)
  
      fn_orig=${file#*C/}
  
      echo "Original file name:" $fn_orig
  
  
  
      #Length of file name
  
      fn_len=${#fn_orig}
  
      echo "Filename Length:" $fn_len
  
  
  
      #file name without path or extension
  
      fn_base=${fn_orig:0:$fn_len-4}
  
      echo "Base file name:" $fn_base
  
  
  
      #new filename suffix
  
      newsuffix=".conv.mp4"
  
  
  
      fn_out=./CONV/$fn_base$newsuffix
  
      echo "Converted file name:" $fn_out
  
  
  
      ffmpeg -i $file -metadata title="$fn_orig" -c:v libx264 -c:a libfdk_aac -b:a 128k $fn_out
  
  
  
      echo "End of iteration"
  
      echo
  
      done
  
  echo "Script completed"

  With the ffmpeg line commented out, and two files in the ./TBC directory, this is the output that I get

      Start of iteration
  
      Full text of file name: ./TBC/Test file with spaces.mp4
  
      Original filename: Test file with spaces.mp4
  
      Filename Length: 25
  
      Base filename: Test file with spaces
  
      Converted file name: ./CONV/Test file with spaces.conv.mp4
  
      End of iteration
  
  
  
      Start of iteration
  
      Full text of file name: ./TBC/Test_file_with_NO_spaces.mp4
  
      Original file name: Test_file_with_NO_spaces.mp4
  
      Filename Length: 28
  
      Base file name: Test_file_with_NO_spaces
  
      Converted file name: ./CONV/Test_file_with_NO_spaces.conv.mp4
  
      End of iteration
  
  
  
      Script completed

  I won’t bother to post the results when ffmpeg is uncommented, other than to state that it fails with the error :
  ./TBC/Test : No such file or directory

  The script then continues to the next file which completes successfully because it has no spaces in its name. The actual filename is "Test file with spaces.mp4" so you can see that ffmpeg stops after the word "Test" when it encounters a space.

  I hope this has been clear and concise and hopefully someone will be able to point me in the right direction. There is a lot more that I want to do with this script such as parsing subdirectories and ignoring non-video files, etc.

  I look forward to any insight you can give !

• Android + ffmpeg + AudioTrack produces bad audio output

  12 septembre 2014, par Goddchen

  here is what I am trying to do : use an AudioRecord and "pipe" the output of AudioRecord.read(byte[],...) to an ffmpeg process’ stdin that will convert to a 3gp (AAC) file.

  The ffmpeg call is as follows :

          ProcessBuilder processBuilder = new ProcessBuilder(BINARY.getAbsolutePath(),
  
                  "-y",
  
                  "-ar", "44100", "-c:a", "pcm_s16le", "-ac", "1","-f","s16le",
  
                  "-i", "-",
  
                  "-strict", "-2", "-c:a", "aac",
  
                  outFile.getAbsolutePath());

  The AudioRecord is setup as follows :

   AudioRecord record = new AudioRecord(/*AudioSource.VOICE_RECOGNITION,*/ AudioSource.MIC,
  
              SAMPLING_RATE,
  
              AudioFormat.CHANNEL_IN_MONO,
  
              AudioFormat.ENCODING_PCM_16BIT,
  
              bufferSize);

  SAMPLING_RATE = 44100 and bufferSize is the one returned by AudioRecord.getMinBufferSize(...)

  I am writing the data to ffmpeg like this :

  try {
  
                          IOUtils.write(data, getFFmpegHelper().getCurrentProcessOutputStream());
  
                      } catch (Exception e) {
  
                          Log.e(Application.LOG_TAG, "Error writing data to ffmpeg process", e);
  
                          //TODO notify user, stop the recording, etc...
  
                      }

  So far so good, the ffmpeg runs and created a proper 3gp file. But the audio in the file is totally off. It seems "choppy" (not sure if this is the correct english word ;) ) and also the pace is wrong, is plays too fast.

  Check out this sample : http://goddchen.de/android/tmp/tmp.3gp

  This is the output of the ffmpeg process :

      [s16le @ 0x23634d0] Estimating duration from bitrate, this may be inaccurate
  
      Guessed Channel Layout for  Input Stream #0.0 : mono
  
      Input #0, s16le, from 'pipe:':
  
      Duration: N/A, start: 0.000000, bitrate: 705 kb/s
  
      Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
  
      [aformat @ 0x2363100] auto-inserting filter 'auto-inserted resampler 0' between the filter 'src' and the filter 'aformat'
  
      [aresample @ 0x235b0a0] chl:mono fmt:s16 r:44100Hz -> chl:mono fmt:flt r:44100Hz
  
      Output #0, 3gp, to '/data/data/com.test.audio/files/tmp.3gp':
  
      Metadata:
  
      encoder         : Lavf54.6.100
  
      Stream #0:0: Audio: aac (mp4a / 0x6134706D), 44100 Hz, mono, flt, 128 kb/s
  
      Stream mapping:
  
      Stream #0:0 -> #0:0 (pcm_s16le -> aac)
  
      size=       3kB time=00:00:00.18 bitrate= 132.5kbits/s    
  
  size=       8kB time=00:00:00.55 bitrate= 120.9kbits/s    
  
  size=      12kB time=00:00:00.83 bitrate= 121.8kbits/s    
  
  size=      16kB time=00:00:01.04 bitrate= 122.8kbits/s    
  
  size=      20kB time=00:00:01.32 bitrate= 122.5kbits/s    
  
  size=      23kB time=00:00:01.53 bitrate= 121.6kbits/s    
  
  size=      27kB time=00:00:01.81 bitrate= 121.0kbits/s    
  
  size=      31kB time=00:00:02.11 bitrate= 120.7kbits/s    
  
  size=      35kB time=00:00:02.32 bitrate= 123.4kbits/s
  
      video:0kB audio:34kB global headers:0kB muxing overhead 3.031610%