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

[Jorge Ramirez]

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!