[vlc-devel] v4l2 in 1.0.0

Pierre Ynard linkfanel at yahoo.fr
Mon Jul 13 19:20:02 CEST 2009

Yesterday I upgraded my Debian and tried to watch TV with my (saa7134)
TV card... v4l2 is a little broken in 1.0.0 compared to 0.9.9a.

First, the driver doesn't accept any chroma, even when passing it

[0x740ba8] v4l2 demux warning: Driver is unable to use specified chroma I420. Trying defaults.
[0x740ba8] v4l2 demux warning: Could not select any of the default chromas; attempting to open as MPEG encoder card (access)

Calls to v4l2_ioctl( i_fd, VIDIOC_S_FMT, &fmt ) fail. It's related to
commit 78e0aba149992ce3685fc1d68d84dbfd881199b6 "Report interlacing in
debug output." which does:

-    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
+    fmt.fmt.pix.field = V4L2_FIELD_NONE;

Putting it back to V4L2_FIELD_INTERLACED solves that issue.

But, second issue, resolution autodetection messes up:

[0x67bf94003f58] v4l2 demux debug: will try to find optimal width and height.
[0x67bf94003f58] v4l2 demux debug: Found maximum framerate of -1,000000
[0x67bf94003f58] v4l2 demux debug: Found optimal dimensions for framerate -1,000000 of 0x0
[0x67bf94003f58] v4l2 demux debug: added new video es I420 48x32

Looks like some unhandled error. When setting the width and height to 0,
the defaults are used correctly.

And, thirdly, the alsa input slave is problematic. The audio plays
normally, but the video is jerky, I get something like 5 fps. If remove
the input slave, the video plays smoothly, and I can play the sound
smoothly too from another VLC.

Pierre Ynard
"Une âme dans un corps, c'est comme un dessin sur une feuille de papier."

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