[Bug 725860] v4l2src: Fix using v4l2src with Hauppauge HDPVR video capture device
GStreamer (bugzilla.gnome.org)
bugzilla at gnome.org
Fri Mar 7 06:31:53 PST 2014
https://bugzilla.gnome.org/show_bug.cgi?id=725860
GStreamer | gst-plugins-good | 1.2.3
--- Comment #11 from Will Manley <gnome at williammanley.net> 2014-03-07 14:54:42 UTC ---
(In reply to comment #9)
> Review of attachment 271165 [details]:
>
> That seems fair, though is this how MPEG support is defined in V4L2 or is this
> only this way for this driver ?
The v4l2 documentation[1] says:
> Identifier Code Details
>
> V4L2_PIX_FMT_MPEG 'MPEG' MPEG stream. The actual format is determined by
> extended control V4L2_CID_MPEG_STREAM_TYPE, see
> Table 1.2, “MPEG Control IDs”.
Table 1.2 in turn says:
> V4L2_CID_MPEG_STREAM_TYPE enum v4l2_mpeg_stream_type
> The MPEG-1, -2 or -4 output stream type. One cannot assume anything here.
> Each hardware MPEG encoder tends to support different subsets of the
> available MPEG stream types. The currently defined stream types are:
>
> V4L2_MPEG_STREAM_TYPE_MPEG2_PS MPEG-2 program stream
> V4L2_MPEG_STREAM_TYPE_MPEG2_TS MPEG-2 transport stream
> V4L2_MPEG_STREAM_TYPE_MPEG1_SS MPEG-1 system stream
> V4L2_MPEG_STREAM_TYPE_MPEG2_DVD MPEG-2 DVD-compatible stream
> V4L2_MPEG_STREAM_TYPE_MPEG1_VCD MPEG-1 VCD-compatible stream
> V4L2_MPEG_STREAM_TYPE_MPEG2_SVCD MPEG-2 SVCD-compatible stream
So currently GStreamer doesn't check V4L2_CID_MPEG_STREAM_TYPE and just assumes
V4L2_MPEG_STREAM_TYPE_MPEG2_TS.
As far as I can see "video/mpegts,systemstream=true" is how mpegts is
represented in terms of GStreamer caps. I do find this confusing as
systemstream=true doesn't seem to confer any additional information. I would
happy to be corrected by someone who knows better though. This systemstream
thing has been puzzling me.
IOW the v4l2 spec doesn't specify any way of having
"video/mpegts,systemstream=false" because the concept only seems to exist in
GStreamer AFAICS and doesn't correspond to any real video or container format.
Therefore it has to be systemstream=true.
[1]:
http://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec-single/v4l2.html#id2809728
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