[FFmpeg-devel] [PATCH] G722 decoder

[Michael Niedermayer]

On Sat, Mar 21, 2009 at 12:43:35AM -0700, Kenan Gillet wrote:
> Hi,
> 
> Here is an implementation of a bitexact G.722 decoder.
> It is based upon the patch G722_decoder_by_Chas_Williams at [1]
> and has been tested against the reference implementation found in ITU-G.711 .
> 
> A sample can be found at /MPlayer/incoming/g722decoder
> In order to play the file, we need to be able force the bitrate from
> the comment line  (patch #1)
> and to use a specific demuxer (patch #2)
> 
> So far I have only found 64kbps / 16Khz raw samples, but i tested the
> other bitrate (48kbps, 56 kbps)
> against the reference implementation
> 
> you can test the uploaded sample with the command:
> ffmpeg -ac 1 -ab 64000 -ar 16000 -i conf-adminmenu-162.g722 output.wav
> 
> Thanks,
> 
> Kenan
> 
> [1] http://wiki.multimedia.cx/index.php?title=Interesting_Patches#G722_decoder_by_Chas_Williams:

> Index: ffmpeg.c
> ===================================================================
> --- ffmpeg.c	(revision 18096)
> +++ ffmpeg.c	(working copy)
> @@ -150,6 +150,7 @@
>  
>  static int intra_only = 0;
>  static int audio_sample_rate = 44100;
> +static int audio_bit_rate;
>  static int64_t channel_layout = 0;
>  #define QSCALE_NONE -99999
>  static float audio_qscale = QSCALE_NONE;
> @@ -2345,12 +2346,14 @@
>  static int opt_bitrate(const char *opt, const char *arg)
>  {
>      int codec_type = opt[0]=='a' ? CODEC_TYPE_AUDIO : CODEC_TYPE_VIDEO;
> +    int bit_rate;
>  
>      opt_default(opt, arg);
>  
> -    if (av_get_int(avcodec_opts[codec_type], "b", NULL) < 1000)
> +    if ((bit_rate = av_get_int(avcodec_opts[codec_type], "b", NULL)) < 1000)
>          fprintf(stderr, "WARNING: The bitrate parameter is set too low. It takes bits/s as argument, not kbits/s\n");
> -
> +    if (codec_type == CODEC_TYPE_AUDIO)
> +        audio_bit_rate = bit_rate;
>      return 0;
>  }
>  

this looks wrong, bit_rate should be available from the AVCodecContext
without this


> @@ -2819,6 +2822,7 @@
>      memset(ap, 0, sizeof(*ap));
>      ap->prealloced_context = 1;
>      ap->sample_rate = audio_sample_rate;
> +    ap->bit_rate = audio_bit_rate;
>      ap->channels = audio_channels;
>      ap->time_base.den = frame_rate.num;
>      ap->time_base.num = frame_rate.den;
> @@ -2892,6 +2896,7 @@
>              channel_layout = enc->channel_layout;
>              audio_channels = enc->channels;
>              audio_sample_rate = enc->sample_rate;
> +            audio_bit_rate = enc->bit_rate;
>              audio_sample_fmt = enc->sample_fmt;
>              input_codecs[nb_icodecs++] = avcodec_find_decoder_by_name(audio_codec_name);
>              if(audio_disable)
> @@ -3211,6 +3216,7 @@
>      }
>      nb_ocodecs++;
>      audio_enc->sample_rate = audio_sample_rate;
> +    audio_enc->bit_rate = audio_bit_rate;
>      audio_enc->time_base= (AVRational){1, audio_sample_rate};
>      if (audio_language) {
>          av_metadata_set(&st->metadata, "language", audio_language);

> Index: libavformat/avformat.h
> ===================================================================
> --- libavformat/avformat.h	(revision 18096)
> +++ libavformat/avformat.h	(working copy)
> @@ -261,6 +261,7 @@
>      enum CodecID video_codec_id;
>      enum CodecID audio_codec_id;
>  #endif
> +    int bit_rate;
>  } AVFormatParameters;
>  
>  //! Demuxer will use url_fopen, no opened file should be provided by the caller.

the whole struct is pretty much deprecated and iam not happy if people
add new things to it.

[...]
> +/**
> + * adpative preditor
> + *
> + * @note On x86 using the MULL macro in a loop is slower than not using the macro.
> + */
> +static void do_adaptive_prediction(struct G722Band *band, const int cur_diff)
> +{
> +    int sg[2], limit, i, cur_part_reconst;
> +
> +    band->qtzd_reconst_mem[1] = band->qtzd_reconst_mem[0];
> +    band->qtzd_reconst_mem[0] = av_clip_int16((band->s_predictor + cur_diff) << 1);
> +
> +    cur_part_reconst = band->s_zero + cur_diff < 0;
> +
> +    sg[0] = sign_lookup[cur_part_reconst != band->part_reconst_mem[0]];
> +    sg[1] = sign_lookup[cur_part_reconst == band->part_reconst_mem[1]];
> +    band->part_reconst_mem[1] = band->part_reconst_mem[0];
> +    band->part_reconst_mem[0] = cur_part_reconst;
> +
> +    band->pole_mem[1] = av_clip((sg[0] * av_clip(band->pole_mem[0], -8191, 8191) >> 5) +
> +                                (sg[1] << 7) + MULL(band->pole_mem[1], 127, 7), -12288, 12288);
> +
> +    limit = 15360 - band->pole_mem[1];
> +    band->pole_mem[0] = av_clip(-192 * sg[0] + MULL(band->pole_mem[0], 255, 8), -limit, limit);

x+= (-x)>>8
coul be used instead of 
x= (x*255)>>8


[...]
> +static int inline scale(const int log_factor, int shift) {
> +    const int wd1 = ilb[(log_factor >> 6) & 31];
> +    shift -= log_factor >> 11;
> +    return shift < 0 ? wd1 << (2-shift) : (wd1 >> shift) << 2;

wd1 << (2-shift) : wd1 >> (shift-2)


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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