[Libav-user] G.711 audio in mkv container

[Alex Grosu]

One correction,

c->frame_size = 2560 (not 2650, typo)

Sorry for this



On 9/23/2016 2:13 PM, Alex Grosu wrote:
> Dear all
>
> I am having some issues in creating a G711 audio mkv container with 
> libavcodec on windows.
> I set the codec context (header) like this:
> c->codec_id = CODEC_ID_PCM_ALAW;
> c->codec_type = CODEC_TYPE_AUDIO;
> c->bit_rate = 64000;
> c->sample_rate = 8000;
> c->channels = 1;
> c->frame_size = 2650;
> c->channel_layout = 1;
> waveFormatEX = malloc(sizeof(WAVEFORMATEXTENSIBLE) + 
> FF_INPUT_BUFFER_PADDING_SIZE);
> waveFormatEX->Format.wFormatTag = WAVE_FORMAT_EXTENSIBLE;
> waveFormatEX->Format.nChannels = 1;
> waveFormatEX->Format.nSamplesPerSec = 8000;
> waveFormatEX->Format.wBitsPerSample = 16;
> waveFormatEX->Format.nBlockAlign = 2;
> waveFormatEX->Format.nAvgBytesPerSec = 16000;
> waveFormatEX->Format.cbSize = sizeof(WAVEFORMATEXTENSIBLE);
> waveFormatEX->Samples.wSamplesPerBlock = 0;
> waveFormatEX->dwChannelMask = KSAUDIO_SPEAKER_MONO;
> waveFormatEX->SubFormat = KSDATAFORMAT_SUBTYPE_ALAW;
> c->extradata = (uint8_t*)waveFormatEX;
> c->extradata_size = waveFormatEX->Format.cbSize;
>
> The mkv container is created, ffplay can play it without problems:
>
> This is the what ffplay outputs when playing the file:
>
> Input #0, matroska,webm, from 'c:\Users\alex\Bus 
> standard-37-Enregistreur Xebra3
> --2016-09-15(0h 1m 0s)\Cam 1 Flux audio.mkv':
>   Metadata:
>     encoder         : Lavf52.78.1
>   Duration: 00:01:52.00, start: 0.000000, bitrate: 34 kb/s
>     Stream #0:0: Audio: pcm_alaw ([6][0][0][0] / 0x0006), 8000 Hz, 1 
> channels, s
> 16, 64 kb/s (default)
>     Stream #0:1(fra): Subtitle: subrip (default)
>    8.94 M-A: -0.000 fd=   0 aq=  421KB vq=    0KB sq=    0B f=0/0
>
> The sound can be heard witthout problems. The file should have ~ 1 
> minute, but ffplay say the duration is 1:52
>
> The vlc player instead has issues in playing the file. The sound is 
> heard but with "gaps", something related to pts?
> This is the info from vlc about the file:
> Type: Audio
> Codec: PCM ALAW(alaw)
> Channels: Mono
> Sample rate: 8000 Hz
> Bits per sample: 16
> And here are some warnings while playing the file:
> corewarning: playback way too early (-170000): playing silence
>
> coredebug: inserting 1360 zeroes
>
> corewarning: playback way too early (-150000): playing silence
>
> coredebug: inserting 1200 zeroes
>
> corewarning: playback way too early (-170000): playing silence
>
> coredebug: inserting 1360 zeroes
>
> corewarning: playback way too early (-150000): playing silence
>
>
>
> Can somebody please guide how to properly set G.711 
> (CODEC_ID_PCM_ALAW) in libavcodec?
> Thank you a lot for reading this long post
>
>
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