[Ffmpeg-devel-old] Re: [Ffmpeg-devel] Speex proposed addition to ffmpeg and suggestions

[Michel Bardiaux]

Dario Andrade wrote:
>  
> 
> Hi Fabrice and ffmpeg maintainers,
> 
>  
> 
> I am developing a Speex (http://www.speex.org) wrapper for the 
> libavcodec, speex.c, and I would like some feedback and/or suggestions:

What is the current state of your project? I know from my archive that 
you were, well not exactly flamed but somewhat singed... for going for 
an external library; but since then, the GSM codec using an external lib 
has been accepted, and anyway mp3lame was already in...


> 
>  
> 
> First of all, if it interests you, I?d love to handle it to you for 
> publishing in the ffmpeg library. In all cases I could use some help and 
> I?d appreciate any feedback:
> 
>  
> 
> 1) In the
> 
>  
> 
> int avcodec_encode_audio(AVCodecContext *avctx,
> 
>                       unsigned char *frame, int buf_size, void *data);
> 
>  
> 
> I wonder if the framesize I am expecting to receive in the ?data? 
> parameter is the same I filled in when user called avcodec_open 
> (ctx->frame_size).
> 
> Should I expect something greater than that? If user sets that in the 
> ctx before opening, may I just encode everything it asks for? In that 
> case, what if the buf_size is not large enough?
> 
>  
> 
> 2) Now the most difficult one: in the
> 
>  
> 
> static int speex_decode_frame(AVCodecContext *avctx,
> 
>                         void *data, int *data_size,
> 
>                         uint8_t* buf, int buf_size)
> 
>  
> 
> I am getting 4096 bytes from ffmpeg.exe when decoding from wav files. 
> What should I expect when decoding it? Should I just decode a single 
> frame and return the number of bytes consumed or should I decode all 
> frames that the ?buf? points to (as long as buf_size is large enough). 
> Note that if I decode everything, I may overflow the ?data? buffer since 
> speex has a very low bitrate encoding.
> 
> If I just return one single frame and the number of bytes consumed, 
> ffmpeg.exe will feed the function with (4096 ? cbLastUsed, i.e. 4096 
> minus the number of bytes I?ve consumed in the last call). That will 
> eventually lead to a call with few bytes available to decode 
> (underflowing my decoder bitstream). In this case, how should I proceed? 
> Should I just return that all bytes have been consumed and set data_size 
> to 0??
> 
>  
> 
> 3) In order to use some advanced speex features as the preprocessor and 
> some codec features, I?ve added the following data types and used some 
> of the AVCodecContext already published:
> 
>  
> 
> AVCodecCtx::level (for the AGC preprocess level)
> 
> AVCodecCtx::noise_reduction (for the denoise preprocessor)
> 
> AVCodecCtx:: rc_max_rate (the maximum VBR bitrate used, i.e. ABR)
> 
> AVCodecCtx:: global_quality (for the speex quality property)
> 
> AVCodecCtx:: flags2 (with the addition of the following constants)
> 
>  
> 
> #define CODEC_FLAG2_AUDIO_PREPROC_AGC       0x01000000 // automatic gain 
> control (encoder or decoder)
> 
> #define CODEC_FLAG2_AUDIO_PREPROC_VAD       0x02000000 // voice activity 
> detection (no activity -> returns 0 bytes encoded)
> 
> #define CODEC_FLAG2_AUDIO_VBR               0x04000000 // variable bitrate
> 
> #define CODEC_FLAG2_AUDIO_DTX               0x08000000 // discontinous 
> transmission (DTX) (no activity -> generates 5 bits/frame, only if vbr 
> or cng enabled)
> 
> #define CODEC_FLAG2_AUDIO_CNG               0x10000000 // confort noise 
> generation (CNG) (no activity (codec vad) -> generates confort noise, 
> always when vbr is enabled)
> 
> #define CODEC_FLAG2_AUDIO_ENH               0x20000000 // perceptual 
> enhancement (ENH) (decoder)
> 
>  
> 
> 4) In order for the speex codec to interpolate frames (in case of a lost 
> packet), I am expecting NULL to the ?buf? parameter when decoding it. 
> That will create a single interpolated frame with no bytes consumed. May 
> I do that? Or should I just use the ?flush? function for that?
> 
>  
> 
> Thanks for any feedback.
> 
>  
> 
> ps: where is the opts.c file?? I love that functionality. Being able to 
> set codec properties (avoptions_parse) by means of a string was one of 
> the best additions to ffmpeg, after the codecs themselves of course. 
> Anyway, I?d love to hear there?s another alternative for that.
> 
>  
> 
> Dario Andrade
> 
> IP.TV
> 
> Mobile +55.21.9453.5005
> 
> Office +55.21.2141.9525
> 
>  
> 


-- 
Michel Bardiaux
Peaktime Belgium S.A.  Bd. du Souverain, 191  B-1160 Bruxelles
Tel : +32 2 790.29.41


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