On Wednesday 11 January 2012 11:05:36 Rupert Eibauer wrote: > Hello, > > I am working on the linux driver for our new video capture board and > facing some compatibility problem which seems to be related to unclear > language in the V4L specification. > > The device supports a larger number of inputs, but with a different set of > standards on each of them. > > Now, the problem is that ffmpeg is using VIDIOC_ENUMSTD/VIDIOC_S_STD > before VIDIOC_S_INPUT. > So the driver has to give a list of supported standards before knowing > which input the device will be taking. > > Currently I am experimenting with a workaround to remember the set > standard and then failing > on VIDIOC_S_INPUT when not compatible, but this seems to create more > problems than it solves. I have > the feeling that this behaviour is not covered by the specification, and > it makes the driver unnecesarily complex. > > In my opinion, the standard is broken: on page > http://v4l2spec.bytesex.org/spec/r11217.htm, it says: > "It is good practice to select an input before querying or negotiating any > other parameters." > It should be changed to "Aplications must...", and ffmpeg needs fixing to > call VIDIOC_S_INPUT before VIDIOC_ENUMSTD. > > I hope to get some opinion from you, if this is the right approach or not. You are correct, it should be 'must' rather than 'good practice'. I've made a patch that updates the text accordingly. I'll post it soon together with some other spec updates. Regards, Hans > > Best regards, > Rupert Eibauer > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
