Hi Rémi, On Wednesday 01 August 2012 10:37:02 Rémi Denis-Courmont wrote: > On Tue, 31 Jul 2012 23:52:35 +0200, Laurent Pinchart wrote: > >> I want to receive the video buffers in user space for processing. > >> Typically "processing" is software encoding or conversion. That's what > >> virtually any V4L application does on the desktop... > > > > But what prevents you from using MMAP ? > > As I wrote several times earlier, MMAP uses fixed number of buffers. In > some tightly controlled media pipeline with low latency, it might work. Sorry about making you repeat. > But in general, the V4L element in the pipeline does not know how fast the > downstream element(s) will consume the buffers. Thus it has to copy from > the MMAP buffers into anonymous user memory pending processing. Then any > dequeued buffer can be requeued as soon as possible. In theory, it might > also be that, even though the latency is known, the number of required > buffers exceeds the maximum MMAP buffers count of the V4L device. Either > way, user space ends up doing memory copy from MMAP to custom buffers. > > This problem does not exist with USERBUF - the V4L2 element can simply > allocate a new buffer for each dequeued buffer. What about using the CREATE_BUFS ioctl to add new MMAP buffers at runtime ? > By the way, this was already discussed a few months ago for the exact same > DMABUF patch series... -- 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
