[pvrusb2] YUV/PCM Format (demux)

[Graham Royston]

On Fri, 9 Jan 2009 12:26:44 +0100
Carsten Meier <cm at trexity.de> wrote:

> Am Thu, 8 Jan 2009 23:04:52 -0500
> schrieb Graham Royston <whiffles at killsbabies.com>:
> 
> > Hello Mike,
> > 
> > With regards to our conversation about retrieving the YUV/PCM
> > information from the PVRUSB2, I've discovered some additional
> > information that I suspect you will find useful. It is as follows:
> > 
> > To reiterate, the commands to pull the information is as follows.
> > They can be sent one at a time, for audio/video only, or one
> > immediately after another for both.
> > // Start sending PCM (instead of sending 0x14 for MPEG)
> > pvr2_encoder_vcmd(hdw,CX2341X_ENC_START_CAPTURE,2,0x01,0x12);
> > 
> > // Start sending YUV
> > pvr2_encoder_vcmd(hdw,CX2341X_ENC_START_CAPTURE,2,0x01,0x11);
> > 
> > 
> > The stream consists of audio and video frames, in no particular
> > order. The audio "frames" are 0x1200 bytes in length (not including
> > the header), the video frames are 0x7E900 in length, and every video
> > frame is followed by some miscellaneous information of 0x120C in
> > length (Something to do with VBI, maybe?). Though, changes in the
> > video resolution or audio bitrate are likely to change those values.
> > 
> > To describe better than I can do in words, I've attached some code
> > for demuxing the streams. It's ugly, but it works. With it, I've
> > been able to play the captured audio and video, albeit with some
> > caveats, described below.
> > Note: It sometimes fails to find the audio header, which makes it
> > not possible to demux the stream. I intended to fix this, but it's
> > getting down to the last minute, and I'm quite sure you're capable
> > of figuring it out. The point is really only to convey the format
> > of the stream. Usage:
> > cat /dev/video0 > captured (CTRL-C, eventually)
> > pvr_demux captured audio_out.raw video_out.yuv
> > 
> > PCM Format:
> > The data is RAW PCM. It appears to be 16-bit, big-endian, but I'm
> > not certain of the frequency. It could possibly be controlled using
> > the same methods as for the MPEG data. Not knowing, or as of yet
> > being able to guess the frequency, the audio is clearly there, but
> > it is distorted (high/low pitched, too fast/slow).
> > 
> > YUV format:
> > The extracted stream can be played in mplayer using the following
> > command:
> > mplayer -rawvideo w=720:h=480:format=hm12 -demuxer rawvideo
> > video.yuv
> > 
> > However, if I use format=hm12, the picture is fuzzy, but not
> > distorted, and the colours are wrong. If I use format=iyuv, the
> > colours are correct, but the picture is distorted. I'm guessing that
> > the colourspace conversion of which you spoke used by the ivtv guys
> > would correct this.
> > 
> > 
> > I hope that is of some assistance. I'd be glad to help out with
> > testing, or anything else that may be necessary.
> > 
> > Thanks,
> > Graham
> 
> Hi,
> 
> do I understand it correctly in that it is possible to get
> uncompressed, raw video and audio data from the pvrusb2? Can it be
> requested from userspace by the normal VIDIOC_S_FMT ioctl?
> 
> Thanks,
> Carsten

Good Day,

It is possible, but not from userspace at the moment, as it is not
implemented by the driver. It requires that the driver be patched to
send different commands and to not look for an MPEG header. My patch to
do so is a quick hack for testing purposes, and is not suitable for
distribution. Also, I don't know if this is possible on all devices and
firmware, but it works on my own (24xxx).

Thanks,
Graham