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• Opening the ALSA microphone port using libavformat

  17 mai 2013, par Kartik Aiyer

  I'm writing a fairly simple application to open the microphone port using the ALSA format on a linux VM. I'm trying to do this using libavformat and other ffmpeg libs ( avutil, avcodec, etc ).

  I followed what ffmpeg was doing ( ffmpeg_opt.c : open_input_file) to open the actual microphone port( hw:0,0). I find the ALSA format using av_find_input_format( "alsa" ) which returns with a AVInputFormat* object.

  I then use this with avformat_open_input.
  I didn't precreate AVFormatContext and load it with any params before the above call ( I rely on it being created in avformat_open_input). This worked and I was able to read packets of the port. However, after a while I was not able to open the port. I added a bunch of debug in the libs and find out that :
  avformat_open_input -> init_input -> ... -> avio_open2 -> ffurl_open ->ffurl_alloc
  the final call to ffurl_alloc goes through all the protocols and tries to see if hw matches any given protocol. This fails.

  I was wondering if anyone has tried opening a mic with the ALSA format using libavformat and other libs, and if they have any tips on how to get this done. Specifically how does ffmpeg translate something like hw:0,0 to the actual device port ?

  P.S : I tried the following line on the command line app
  ffmpeg -f alsa -i hw:0,0 -ac 2 -acodec pcm_s16le output.aac
  this worked for a while and then suddenly stopped working as well with the same kind of problem. Unable to open the protocol.

  I'm not sure what changed and why its not able to open the audio port, but any advice on how also port are opened with the rather different handle of HW:x,x would be much appreciated.

  Alternatively, I realize ffmpeg is a little heavy to just read PCM packets and then encode and I could use a more direct approach by using the aac libs directly. Can anyone recommend a lib or kernel driver that I can use to open the microphone ( given that it is an ALSA card )and read PCM data out of it. ( I'm new to LInux so please forgive me if any of this sounds trivial )

  Thanks
  Kartik

• Evolution #2812 : Avertir de l’absence de SQLite sur la page de backup

  12 mai 2013, par cedric -

  @Thierry : Les warning sur l’unicité des clés primaires sont "normaux" dans le sens où ils permettent de se protéger vis à vis de l’approximation inhérente à la reprise sur interruption. Les backups au format XML des versions précédentes avaient les mêmes défauts mais sans protection de ce côté là, conduisant à des données erronées au final.
  L’absence de table meta a la connexion est aussi normale lors du backup.
  Le fait que ce soit lent est lui inhérent au mode de sauvegarde où l’on lit les tables morceau par morceau pour les écrires dans un fichier (que ce soit SQLite ou XML ne change rien sur ce point).

  Et bien sur, mysqldump est bien plus rapide, de plusieurs ordres de grandeur. Mais le format SQL qu’il produit n’est pas portable, pose parfois des problèmes au ré-import sur un autre serveur avec une version mySQL différente, et n’est pas importable dans un SQLite par exemple.

  Bref pas de solution idéale, encore une fois celle proposée dans le core essaye d’être le plus générique possible.

• Using Coldfusion's CFFILE tag to monitor a progress log from FFMpeg

  5 mai 2013, par user1493918

  I want to learn how to use the CFFILE tag from ColdFusion to read the contents of a text file. In my case, that text file is a progress log that is generated by FFMpeg while it transcodes a media file. I want to write a ColdFusion script that will poll the progress log periodically, until the log indicates that FFMpeg has finished its transcoding operation. On the client side I can then use Ajax to hit that ColdFusion script and show the user a "percentage completed" while FFMpeg does its work.

  I got FFMpeg to generate the log file by using a new "progress" flag that recent versions of FFMpeg now support. Below I'll show you the way to use this flag, and also the generated output within the log file.

  Here's the FFMpeg command :

  ffmpeg -i c:\my_original_file.ogg c:\my_converted_file.mp3 -progress c:\my_progress.txt

  The above command will cause FFMpeg to generate a log file called my_progress.txt.

  Here's what it generates in the log file :

  total_size=206150
  
  out_time_ms=51410044
  
  out_time=00:00:51.410044
  
  dup_frames=0
  
  drop_frames=0
  
  progress=continue

  The above 6 lines are generated repeatedly in the log file, with increasing values.

  total_size=206150
  
  out_time_ms=51410044
  
  out_time=00:00:51.410044
  
  dup_frames=0
  
  drop_frames=0
  
  progress=continue
  
  total_size=412413
  
  out_time_ms=102975756
  
  out_time=00:01:42.975756
  
  dup_frames=0
  
  drop_frames=0
  
  progress=continue
  
  total_size=618363
  
  out_time_ms=154463111
  
  out_time=00:02:34.463111
  
  dup_frames=0
  
  drop_frames=0
  
  progress=continue
  
  total_size=824939
  
  out_time_ms=206107189
  
  out_time=00:03:26.107189
  
  dup_frames=0
  
  drop_frames=0
  
  progress=continue

  Finally, when the job completes, the final block of 6 lines are the last ones in the log file. Notice the "progress=end" on the last line :

  total_size=9725902
  
  out_time_ms=2431348011
  
  out_time=00:40:31.348011
  
  dup_frames=0
  
  drop_frames=0
  
  progress=end

  I want to write a Coldfusion script using the CFFILE tag to read only the last 6 lines of the file (no matter how large the file has become), and to do this each time the script is called, by the browser, via Ajax. Finally I need to parse the values on these lines into variables so I can return some data to the caller.

  I've researched progress bars for FFMpeg but they're in PHP which is hard for me, and besides, they parse the older formatted versions of FFMpeg's log files, and I would like to use the above newer formatting. Can anyone please help ?