[pvrusb2] YUV/PCM Format (demux)

[Carsten Meier]

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