[Libav-user] libvorbis encoder problem

[Tomaž Rotovnik]

> Hi
>
> I checked *doc/examples/muxingc.c* file where an example generating MPEG
> AV file is explained. Then I try to change AV format to "*webm*" (video
> is encoded with VP8 and audio with vorbis encoder). I have problems with
> setting the right parameters for vorbis encoder. When I debugging through
> the code I figured out that vorbis only accepts (AV_SAMPLE_FMT_FLTP) sample
> format type. Example was done with (AV_SAMPLE_FMT_S16). I looked into
> source code to figure out that when I call
>
> *av**codec_fill_audio_frame(AVFrame, channels, sample_format, buffer,
> buf_size, align)*,
>
> in case of AV_SAMPLE_FMT_FLTP the buffer should be type *float** and
> audio samples should have values between -1.0 to 1.0. For more than one
> channel values are *not interleaved *(FLTP - float plain) but they are
> followed by each other (array: all values for channel0, all values for
> channel 1, ...).
>
> When I accept those changes in my code, unfortunately I still don't get
> correct result. If I use mono (1 channel only) then the flag (got_packet)
> returned from function *avcodec_encode_audio2* is set only once (after
> around 5 consecutive calls), with *AVPacket->pts* timestamp set to some
> huge values. Because of that only video is encoded.
> When I set stereo mode I get error from function *
> av_interleaved_write_frame* (-12).
>
> I tested the same code and setting AV format to "*asf*", where audio is
> encoded with WMA2 encoder and also accepts AV_SAMPLE_FMT_FLTP sample format
> type. I got correct AV file which can be played with VLC player or Windows
> media player.
>
> I think I still need to set some flags for vorbis encoder, but I can't
> figure out. I would appreciate any suggestions.
>
> Best regards
>
> For audio encoder I set those parameters:
>
> c->sample_fmt = AV_SAMPLE_FMT_FLTP;
> c->sample_rate = 44100;
> c->channels = 1;
>
> My code to prepare samples in AV_SAMPLE_FMT_FLTP sample format:
>
> void TT_Transcode::get_audio_frame_fltp(float *fsamples, int frame_size,
> int nb_channels)
> {
>     int j, i;
>     float v;
>     float *q;
>     for (j = 0; j < frame_size; j++) {
>         v = (sin(t) * 10000.0) / 32767.0f; //values between -1.0 and +1.0
>         fsamples[ j ] = v;
>         for (i = 1; i < nb_channels; i++)
>         {
>             fsamples[i * in_linesize + j] = v;
>         }
>         t += tincr;
>         tincr += tincr2;
>     }
> }
>
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