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

Hendrik Leppkes h.leppkes at gmail.com
Wed Dec 30 00:33:30 CET 2015

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:
>> with subtype
>> 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.

- Hendrik

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