[FFmpeg-devel] [GSoC] BDA (DTV) Capture / tuning -- work-in-progress

[Hendrik Leppkes]

On Wed, Dec 30, 2015 at 12:33 AM, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> On Wed, Dec 30, 2015 at 12:23 AM, Roger Pack <rogerdpack2 at gmail.com> wrote:
>>> OK I had this great idea to capture the incoming MPEG2 transport
>>> stream from the digital TV capture device.  Kind of like "raw" stream,
>>> so FFmpeg could have access to, for instance, all the audio stream.
>>>
>>> It appears that the type coming out of the tuner is:
>>> MEDIATYPE_Stream
>>> with subtype
>>> KSDATAFORMAT_SUBTYPE_BDA_MPEG2_TRANSPORT
>>> which is apparently treated the same as MEDIASUBTYPE_MPEG2_TRANSPORT
>>> by the built in directshow mpeg demuxer [1] so I assume is some kind
>>> of typical MPEG2 TS stream.
>>>
>>> I had hoped that if I set dshow's AVStream's codec_id to
>>>          codec->codec_id = AV_CODEC_ID_NONE;
>>>          codec->codec_type = AVMEDIA_TYPE_DATA;
>>
>> Oops that was meant to be
>>
>>             codec->codec_id = AV_CODEC_ID_MPEG2TS;
>>             codec->codec_type = AVMEDIA_TYPE_DATA;
>>
>>> That it would somehow recognize that I was sending it an MPEG stream
>>> and insert an appropriate demuxer for me.
>>>
>>> However, when I run it, it fails like this:
>>>
>>> Input #0, dshow, from 'video=Hauppauge WinTV 885 BDA Tuner/Demod':
>>>   Duration: N/A, bitrate: N/A
>>> Codec 0x20000 is not in the full list.
>>>     Stream #0:0, 0, 1/27000000: Data: unknown_codec, 0/1
>>> Successfully opened the file.
>>> Output #0, mp4, to 'yo.mp4':
>>> Output file #0 does not contain any stream
>>>
>>> so it's definitely not, for instance, doing a probe or analyze on the
>>> MPEG stream....
>>>
>>> Is this possible or any hints/tips/tricks I could possibly use?
>>
>> To answer my own question, I turned the dshow capture device into both
>> an AVInputFormat *and* a URLProtocol that "wraps" the AVInputFormat.
>> Apparently ffmpeg can receive "raw" bytes only from URLProtocol (?)
>> This way worked great both "segmented" MPEG2VIDEO streams as well as
>> "raw" MPEG TS streams.
>>
>
> You should probably just make it use the mpegts demuxer directly, say
> like the rtsp demuxer.
> We have an API for that in the form of avpriv_mpegts_parse_packet
>
> Making an input device a protocol seems rather ugly, the user needs to
> know beforehand how to call it that way.
>

Or as an alternative, why not just add the mpegts demuxer to the DShow
graph as well and directly get video/audio streams.
For Live TV functionality, the MS demuxer seems to be working quite well.

- Hendrik