[Ffmpeg-devel] [PATCH] MS-GSM support: draft for review

[Michel Bardiaux]

Benjamin Larsson wrote:
[snip]

>>>    
>>>
>>>> your implementation does not allow -acodec copy between msgsm<->gsm
>>>>      
>>>>
>>> There are other diffrences that won't allow this, just not the double 
>>> packing of frames. For this to work the stream would need to pass a 
>>> bitstream filter also. 
>>>    
>>>
>> could you elaborate on the other things needed? i thought ms just
>> packed 2frames together?
>>  
>>
> 
>>From http://kbs.cs.tu-berlin.de/~jutta/toast.html
> 
> "Microsoft's GSM 06.10 CODEC is not compatible with toast's frame format
> - they use 65-byte-frames (2 x 32 1/2) rather than rounding to 33, and
> they number the bits in their bytes from the other end. (Well done, guys.)"

Aargh, I knew that once, then Jutta Degener's group came out with 
internal support for MS-GSM, you only had to remember you have to 
advance sometimes by 32 sometimes by 33 bytes; the bit part of course I 
forgot.

> 
> Doing a bitstream filter for that would mean writing a complete
> bitstream parser for the format.
> 

What about considering this is a WAV-only thing and do everything in 
wav_read/write_packet? Seeking, of course, would be a little more 
acrobatic then with PCM.

-- 
Michel Bardiaux
R&D Director
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