[Ffmpeg-devel] VC-1 stream handling

Michael Niedermayer michaelni
Mon Jan 15 23:34:32 CET 2007


On Mon, Jan 15, 2007 at 04:36:34PM +0000, Ian Caulfield wrote:
> Hi,
> I've been working on adapting FFmpeg to handle VC-1 elementary streams, as
> well as muxing/demuxing VC-1 in MPEG-PS. I've written the PS muxing/demuxing
> code, but currently I'm having a problem getting the vc1 codec to handle it,
> as currently the vc1 codec is set up to work with WVC1 streams in ASF, which
> have the picture startcodes stripped and the sequence header stored in
> extradata. I'm just wondering what the best way to handle this would be.
> - The VC-1 decoder code could be modified to handle a VC-1 bitstream as well
> as the current stripped format from ASF, but it wouldn't be possible to do
> MPEG<->WMV remuxing of VC-1 streams

there are bitstream filters to insert and remove the contents of extradata
into the bitstream ...

you could also write one which changes the exact format ...

> - The ASF parser could reassemble the elementary stream (stick the headers
> >from extradata on the front, add 0000010d before each picture) - I knocked
> up some rough code to do this to allow VC-1 demuxing from asf, but this
> still requires modifications to the vc1 codec, and introduces some
> codec-dependent code into the asf demuxer, which isn't very pleasant.

vc1 dependant code in (de)muxers is likely not going to be acepted unless
there is no other way to solve the issues ...
look at libavcodec/parser.c and libavcodec/bitstream_filter.*

note, one thing the bitstream filters lack currently is automatic filter
insertion ...

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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