[Ffmpeg-devel] Newbie question about pcm_s16le

michele tavella michele
Fri Aug 4 10:18:53 CEST 2006

Dear all, 
I subscribed to ffmpeg-devel two days ago. I'm working on my master
thesis and (as the first task) I have to synchronize two streams:
- a standard DV stream
- a PCM audio stream

I understand that my question could be off-topic, so I'm sorry if I
bother you, but it is the first time I approach the audio/video field.

I'm currently using the FFMPEG API to handle decoding of a DV Raw
stream acquired via "dvgrab" (dvvideo + stereo pcm_s16le).

Following the examples I did find googling around, I have successfully
decoded the video frames.

I've also decoded the PCM stream and I can handle the stream as a
vector of shorts.

On a couple of guides said that the PCM stream should alternate Left
channel samples with right channel samples, something like this:
Channel	L R L R L R ...
Index	0 1 2 3 4 5 ...

In image_001.png you can find a plot of the even and the odd samples of
an audio frame.

The Odd Samples signal looks to me like a synchronization signal! 
I'm now wondering how the stream is organized. 

Any help would be great, also in terms of documentation/books.

Thank you for your time, 


     home  tavella.michele at gmail.com	
 LIRA-Lab  michele at liralab.it 
  OpenPGP  98E66CEC
      web  http://mt.homelinux.org 

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