How to develop a new unsupported fourcc decoder

[bharmel]

Hi,

I'm discovering out of tree Vlc plugin development and it is great !
I have written a demux plugin which can split my proprietary AudioVideo (AV) ip stream.
This ip stream contains 2 elementary streams:
- One video MJPEG stream
- One text metatdata stream.

My demux creates these 2 objects with:
es_format_Init(&pSys_X->VideoFormat_X,VIDEO_ES,0);
pSys_X->VideoFormat_X.i_codec=VLC_CODEC_MJPG;
pSys_X->pEsVideo_X=es_out_Add(pDemux_X->out,&pSys_X->VideoFormat_X);
and:
CodecFourCC_X=VLC_FOURCC('k','t','c','1'); //In-house format, not supported by vlc
es_format_Init(&pSys_X->TcFormat_X,SPU_ES,CodecFourCC_X);
pSys_X->pEsTc_X=es_out_Add(pDemux_X->out,&pSys_X->TcFormat_X);

When the demux receive our proprietary AV ip stream it outputs blocks with the corresponding data with:
block_t *pBlock_X;

Video:
es_out_Control(_pDemux_X->out,ES_OUT_SET_PCR,pBlock_X->i_pts);
es_out_Send(_pDemux_X->out,pSys_X->pEsVideo_X,pBlock_X);
Text:
es_out_Send(_pDemux_X->out,pSys_X->pEsTc_X,pBlock_X);

All the different payload are correcty setuped in the pBlock_X structure

So far so good, everything seems ok.

My questions are:
- Which king of module do I need to create to consume the text stream which is produced by es_out_Send(_pDemux_X->out,pSys_X->pEsTc_X,pBlock_X) ? (I don't want to use standard Vlc module because I need to make extra work on the text payload)
- How Vlc makes the link between my new codec fourcc code and the module which can handle its processing ? (In my case CodecFourCC_X=VLC_FOURCC('k','t','c','1'); //In-house format, not supported by vlc)
- By looking in Vlc source it seems that the association between codec fourcc code and codec module is stored in a static array. Is that right ?
- Is there any documentation or examples of a module which produce a custom elementary stream and another module which consume it ? !! these modules should produce and process out of the shelf unsupported data type (no MJPEG or MP3 but a 'new' unsupported format)
- If I just want to display my text metadata stream as a "marquee", is it possible to consume the text stream using a standard vlc module (!!! text data can chand up to 60 times per seconds !!)

Thank you very much for your time and help

Best regards

[Rémi Denis-Courmont]

You need to write a decoder plugin and match the i_fourcc in the input format.

[bharmel]

Hi,

thank you for your reply. I start to develop a decoder:
#define MODULE_STRING "KatTcCodec"
vlc_module_begin ()
set_description( N_("KatTc decoder") )
set_capability( "decoder", 0 )
set_callbacks( KATTCCODEC_Open, KATTCCODEC_Close )
set_category(CAT_INPUT)
set_subcategory(SUBCAT_INPUT_SCODEC)
vlc_module_end ()

int KATTCCODEC_Open(vlc_object_t *_pThis_X)
{
int Rts_i=VLC_ERR_INVALIDPARAM;
decoder_t *pDecoder_X=NULL;

if (_pThis_X)
{
pDecoder_X=(decoder_t *)_pThis_X;
msg_Dbg(pDecoder_X,"KATTCCODEC_Open(%X) Codec 0x%08X",_pThis_X,pDecoder_X->fmt_out.i_codec);
...


When i start my vlc based application, I can see the video but no metadata.

If I look to the Vlc log file I cannot see the message which is displayed in my KATTCCODEC_Open function (msg_Dbg(pDecoder_X,"KATTCCODEC_Open(%X) Codec 0x%08X",_pThis_X,pDecoder_X->fmt_out.i_codec);)
and no vlc log about foreign fourcc code or codec lookup....

The libvlc engine does not seem to look for a decoder for my special fourcc code and I have checked that this one is really present in the output stream (by using the Vlc media player interface Tools->Media Information->Codec)

????

[bharmel]

Hi,

When I try to activate my elementary stream with fourcc code ktc1 I got this error message on my screen:

No suitable decoder module:
VLC does not support the audio or video format "ktc1". Unfortunately there is no way for you to fix this.

==> Vlc seems to say that it is not possible....

Is a normal/true/.... ????

[diman23]

==> Vlc seems to say that it is not possible....

everything is possible
are you implementing on windows or linux?
out of tree right?
did you check if your decoder appear in plugin list? (could VLC load your dll/so)

I saw that you set score to 0. set_capability( "decoder", 0 ). did you enable your module with --codec?