[FFmpeg-devel] [Ffmpeg-devel] [PATCH] GSM-MS decoder and encoder

[Baptiste Coudurier]

Hi,

Michel Bardiaux wrote:
> Baptiste Coudurier wrote:
>> Michael Niedermayer wrote:
>>> Hi
>>>
>>> On Mon, Feb 19, 2007 at 11:59:14AM +0100, Michel Bardiaux wrote:
>>>> Michael Niedermayer wrote:
>>>>> Hi
>>>>>
>>>>> On Sat, Feb 17, 2007 at 03:42:52PM +0100, Michel Bardiaux wrote:
>>>>>> Michael Niedermayer wrote:
>>>>>>> Hi
>>>> [snip]
>>>>>>> is 13000 exactly correct isnt it 13200 for CODEC_ID_GSM?
>>>>>> Yes and no. The last 4 bits of each frame are not actually used, they
>>>>>> come on stage only because we (both libgsm and lavc) use a
>>>>>> byte-oriented
>>>>>> API, and files made of bytes. They should be considered as container
>>>>>> overhead in TOAST files, hence not part of the codec bitrate.
>>>>> but with this argumentation we would have to subtract the padding
>>>>> bits from
>>>>> mpeg from the bitrate too and thats something we dont 
>>>> I think you're talking codec-level padding here, but I wrote of
>>>> container overhead.
>>>>
>>>>> also it would cause
>>>>> problems for containers which expect the bitrate well to be the
>>>>> bitrate of
>>>>> what they get, not to be slightly less due to some padding bits
>>>>> they dont
>>>>> know about ...
>>>> AFAIK currently only some MS containers (AVI, WAV) accept GSM, and
>>>> then only MS-GSM, which does not have the problem. The only
>>>> container for non-MS-GSM is TOAST (currently not implemented) and
>>>> that one knows about the 4 extra bytes.
>>> well a grep for gsm shows a hit in aiff.c so it seems it is supported
>>> in a
>>> non toast format currently and as there is no gsm specific code in it
>>> i would
>>> guess it will end with 13200 as bitrate
>>>
>>> anyway i wont fight about this appl the patch, i will remove the
>>> 13000 check
>>> when it breaks something
>>>
>>
>> I was fixing agsm in mov, and this bitrate check cause init to fail for
>> decoding (encoding shares the function), IMHO we don't care about
>> bitrate when decoding.
>>
>> Can I remove it ?
>>
> Oops, forgot I am maintainer for libgsm!
> 
> Since bitrate is also irrelevant for encoding, what about this?
> 
> 
> ------------------------------------------------------------------------
> 
> Index: libavcodec/libgsm.c
> ===================================================================
> --- libavcodec/libgsm.c	(revision 12579)
> +++ libavcodec/libgsm.c	(working copy)
> @@ -36,8 +36,10 @@
>  #define GSM_FRAME_SIZE 160
>  
>  static av_cold int libgsm_init(AVCodecContext *avctx) {
> -    if (avctx->channels > 1 || avctx->sample_rate != 8000 || avctx->bit_rate != 13000)
> +    if (avctx->channels > 1 || avctx->sample_rate != 8000)
>          return -1;
> +    if (avctx->bit_rate != 13000)
> +        av_log(avctx, AV_LOG_WARNING, "Bit rate %d instead of expected 13000 - ignored\n");
>  

Well, Im not really ok to annoy user with a false message, when decoding
this is irrelevant.

What is this check good for, since bitrate is irrelevant ?

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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