[FFmpeg-devel] [PATCHv6 4/4] libavcodec: v4l2: add support for v4l2 mem2mem codecs

[wm4]

On Tue, 29 Aug 2017 15:11:55 +0200
Jorge Ramirez <jorge.ramirez-ortiz at linaro.org> wrote:

> On 08/25/2017 05:35 PM, wm4 wrote:
> >> +static inline void set_pts(V4L2Buffer *out, int64_t pts)
> >> +{
> >> +    if (pts == AV_NOPTS_VALUE) {
> >> +        /* invalid timestamp: not sure how to handle this case */
> >> +        out->timestamp.tv_sec  = 0;
> >> +        out->timestamp.tv_usec = 0;
> >> +    } else {
> >> +        AVRational v4l2_timebase = { 1, 1000000 };
> >> +        int64_t v4l2_pts = av_rescale_q(pts, out->context->time_base, v4l2_timebase);
> >> +        out->timestamp.tv_sec  = v4l2_pts / INT64_C(1000000);
> >> +        out->timestamp.tv_usec = v4l2_pts % INT64_C(1000000);
> >> +    }
> >> +}  
> > Why does it require a fixed timebase? A decoder shouldn't even look at
> > the timestamps, it should only pass them though. Also, not using DTS
> > will make it a nightmare to support containers like avi.
> >
> > I suspect the decoder tries to "fix" timestamps, or maybe even does
> > something particularly bad like reordering frames by timestamps. This
> > is NOT something that should be in a kernel API.
> >
> > (FFmpeg native decoders_and_  hwaccels pass through both PTS and DTS,
> > and don't touch their values.)
> >  
> 
> ok I will just pass through the dts/pts and return them unmodified for 
> decoding and retest.
> 
> what about for encoding? should I just read the pts from the driver, 
> rescale it back to time_base and set both pts&&dts on the returned 
> packet to the this same value?
> 
> after this I think I am ready to post v7 with all the review comments 
> addressed so thanks a lot for all the responses!

Things are different from encoders. These should synthesize correct pts
and dts from the pts set on input frames.