Hi Alain, On Wednesday 31 October 2012 14:21:30 Alain VOLMAT wrote: > Hi all, > > We have developed a V4L2 mem2mem driver for an H264 encoder running on an IP > of one of our SoC and would like to have one more v4l2_buffer flag value > for that. > > In the context of this driver, we discovered that the current V4L2 encode > API is missing the feature to mention to the IP that a time discontinuity > has to be created. Time discontinuity must be triggered when there is a > discontinuity in the stream to be encoded, which would for example happen > when there is a seek in the data to be encoded. In such case, it means that > the IP should reset its bitrate allocation algorithm. > > Considering that this information should be triggered on a frame basis, the > idea is to have it passed via the flags member of v4l2_buffer, with a new > flag V4L2_BUF_FLAG_ENCODE_TIME_DISCONTINUITY. > > The usage for this flag value are: > * Queuing a "to be encoded" v4l2_buffer with flags & > V4L2_BUF_FLAG_ENCODE_TIME_DISCONTINUITY informs the driver/IP that a time > discontinuity (reset in the bitrate allocation algorithm) should be > performed before encoding this frame. * The flags bit should be then > propagated until the dequeue to let the application know when a buffer is > the first one after a time discontinuity. I wonder whether a buffer flag is the best technical solution for this. There's a very limited quantity of flags, and it seems to me like we'll need more flags like this one in the future. Using flags thus wouldn't scale. Encoding a frame obviously requires the contents of the frame itself, but also requires meta data such as time discontinuity. Would it be better to add a meta data plane that would be used to pass all the frame meta data to the encoder ? > Few words about the driver itself, it is available in the following context. > 1. STLinux kernel (www.stlinux.com) rather than vanilla kernel since the > board support is only available there for now 2. Multicom > (http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/US > ER_MANUAL/CD18182595.pdf) based V4L2 driver. Multicom is an ST layer to > allow to send and serialize commands to our various IP. -- Regards, Laurent Pinchart -- 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
