On Thu, 19. Aug 16:55, Ming Qian wrote:
> there are two proper ways to setup capture queue.
> 1. client wait the source change event,
> then setup the capture queue and streamon
> 2. client setup the capture queue in advance,
> but to avoid time issues, client should start
> the capture queue before it enqueue the sequence
> header to decoder driver through output queue.
> and the sequence header is always in the first
> frame, so client should start capture before
> enqueue the first frame.
>
> ffmpeg use the method 2 to setup capture queue,
> but currently ffmpeg enqueue the first frame
> before starting the capture queue.
> so in driver side, there are time issues.
> when driver has parsed the resolution from sequence header,
> but the client may not finished setup the capture.
> so driver can't decide whether to notify a source change event to
> client. and the following flow may be chaotic.
>
> And it's OK that client setup capture queue first, then enqueue the
> first frame.
>
> Signed-off-by: Ming Qian <ming.q...@nxp.com>
> ---
> libavcodec/v4l2_m2m_dec.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/libavcodec/v4l2_m2m_dec.c b/libavcodec/v4l2_m2m_dec.c
> index 224eb3d5e7be..6b936b6df2a9 100644
> --- a/libavcodec/v4l2_m2m_dec.c
> +++ b/libavcodec/v4l2_m2m_dec.c
> @@ -149,6 +149,14 @@ static int v4l2_receive_frame(AVCodecContext *avctx,
> AVFrame *frame)
> if (s->draining)
> goto dequeue;
>
> + ret = v4l2_try_start(avctx);
> + if (ret) {
> + /* can't recover */
> + if (ret != AVERROR(ENOMEM))
> + ret = 0;
> + goto fail;
> + }
> +
> ret = ff_v4l2_context_enqueue_packet(output, &s->buf_pkt);
> if (ret < 0 && ret != AVERROR(EAGAIN))
> goto fail;
> @@ -157,16 +165,6 @@ static int v4l2_receive_frame(AVCodecContext *avctx,
> AVFrame *frame)
> if (ret != AVERROR(EAGAIN))
> av_packet_unref(&s->buf_pkt);
>
> - if (!s->draining) {
> - ret = v4l2_try_start(avctx);
> - if (ret) {
> - /* cant recover */
> - if (ret != AVERROR(ENOMEM))
> - ret = 0;
> - goto fail;
> - }
> - }
> -
> dequeue:
> return ff_v4l2_context_dequeue_frame(capture, frame, -1);
> fail:
Unfortunately this does not work on odroid xu4.
It needs to parse the parameter sets before VIDIOC_G_FMT ioctl is called on the
capture queue:
https://github.com/hardkernel/linux/blob/odroid-5.4.y/drivers/media/platform/s5p-mfc/s5p_mfc_dec.c#L317
Thanks,
--
Andriy
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