[pvrusb2] YUV/PCM Format (demux)

[Carsten Meier]

Am Fri, 9 Jan 2009 07:12:29 -0500
schrieb Graham Royston <whiffles at killsbabies.com>:

> 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

It would be very cool if such a feature is available. Then I can decode
PAL-Plus signals in software and encode it with Dirac without loss of
quality.

I'm looking forward... :)

Carsten