[FFmpeg-devel] 回复: [EXT] Re: [PATCH] avcodec/v4l2_buffers: don't prevent enqueue capture buffer to driver

[Andriy Gelman]

On Thu, 09. Apr 00:27, Andriy Gelman wrote:
> On Thu, 09. Apr 02:14, Ming Qian wrote:
> > Did you try increasing the -num_capture_buffers option? It may solve your problem.
> > 1. We can't increase the num_capture_buffers indefinitely.
> > 2. There is a ring buffer in driver, so the number of frames who is stored in the ring buffer may be a large value, This depends on the speed of the input and output. So it's likely that when output port is done, there are a large count of frames who have not been decoded,  if the capture port prevent qbuf to driver, there will no frame buffer to store the decoded frame.
> > 
> > There is currently a check that sets ctx->done=1 when all the capture buffers are dequeued (v4l2_context.c:300), and this patch would prevent it (although it's not needed if an eos event is received).
> 
> > Yes, but I think it's not appropriate to judge whether the capture port is done by checking all the capture buffers are dequeued.
> > 
> 
> I tend to agree with you. Even if eos event is not setup/supported, we should
> be able to set ctx->done=1 via the EPIPE error.  
> 
> But let's wait for some more comments. 
> 

In [1] it says that capture buffers should be enqueued back to the device while
draining.

I'll apply this patch on Wednesday if no one objects.


[1] https://patchwork.kernel.org/patch/11110031/

"...The client must continue to handle both queues independently,
   smilarly to normal encode operation. This includes:

   * queuing and dequeuing ``CAPTURE`` buffers, until a buffer marked with the
     ``V4L2_BUF_FLAG_LAST`` flag is dequeued, ... " 

-- 
Andriy