[vlc-devel] [PATCH] v4l2 mpeg2 controls

Dennis Lou dlou99 at yahoo.com
Tue Jan 8 21:37:08 CET 2008

>From: Antoine Cellerier <dionoea at videolan.org>
>Are all MPEG parameters pre-stream? or can some still be changed while
>the stream is playing (like if you want to tweak the bitrate a bit or
>some encoder setting)? (I'd have to get an MPEG encoding card to test)

On my blackbird card they're all pre-stream only.  I'll plug in my ivtv card, but I have a feeling that will be pre-stream only as well.

[adding volume/balance/mute]
>Is there any reason why you left the 3 other audio controls out? (I
>didn't include audio controls in the first place since I didn't know if
>they were used by any v4l2 driver ...)

These three are implemented in my driver while the other 3 are not. I tossed those in to quiet the msg_Err's it was spewing.

>> +static void ControlDebugPrint( vlc_object_t *p_obj, int i_fd,
>Wouldn't it be possible to somehow merge this function with
>ControlListPrint ? (as far as I can see it's the same function without
>any of the VLC variables creation code)

Yes, I started to do this but it was looking messy.

>The --v4l2-reset-controls switch options isn't taken into account for
>MPEG class controls.

Correct.  This ought to be fixed.

BTW, I took a look at the QT4 code.  In open_panels.cpp, it would probably be prudent to CONNECT() the lostFocus() signal of the v4l2VideoDevice QLineEdit to a function that probes the video device and retrieves the avail_ctrls linked list from v4l2's demux_sys_t and builds the "Advanced Options" dialog that way, perhaps by destroying unavailable controls.  The V4L2 Advanced Options is rather large on my machine and filled with parameters unavailable to my device.  If you want, I can get to coding this.


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