[Freeswitch-dev] Video synchronization

[Anthony Minessale]

without threads for both it would require doing non blocking reads on the
rtp streams.
We have some provisions in the code for being able to do this but I am not
sure it's been proven to work.
We can always try to dust it off.

I think its done by passing the io_flag SWITCH_IO_FLAG_NOBLOCK to the
read_frame call.

Another idea would be to open the audio and video tracks separately each in
it's own thread and play them independently since it's 2 different IP
streams.



2010/7/13 Paulo Rogério Panhoto <paulo at voicetechnology.com.br>

>      I've found a way to synchronize the A/V streams with usleep() but I
> don't think that's the best way to do this. Is there a switch_core....
> function to perform a similar task (and maybe allow other tasks to run)?
>
>     Here's the current version of the playback loop (that takes into
> consideration multiple RTP packets per video frame) :
>
>         u_int64_t videoNext = 0, audioNext = 0;
>         u_int64_t ts = 0;
>
>         bool videoSent = true, audioSent = true;
>
>         while (switch_channel_ready(channel))
>         {
>             bool vOk, aOk;
>             if(videoSent)
>
>             {
>                 vid_frame.packetlen = vid_frame.buflen;
>                 vOk = vc.getVideoPacket(vid_frame.packet,
> vid_frame.packetlen);
>                 if (vOk)
>                 {
>                     switch_rtp_hdr_t *hdr =
> reinterpret_cast<switch_rtp_hdr_t *>(vid_frame.packet);
>
>                     videoNext =
> vc.videoTrack().track.get90KTimestamp(ntohl(hdr->ts));
>                     hdr->ts = htonl(videoNext);
>
>                     if (pt)
>                         hdr->pt = pt;
>                 }
>                 videoSent = false;
>             }
>             if(audioSent)
>
>             {
>                 write_frame.datalen = write_frame.buflen;
>                 aOk = vc.getAudioPacket(write_frame.data,
> write_frame.datalen);
>                 audioSent = false;
>             }
>
>             if (!vOk && !aOk)
>                 break;
>
>
>             int64_t wait = min(audioNext, videoNext) - ts;
>             if(wait > 0)
>             {
>                 /* wait the time for the next A/V frame */
>                 usleep(wait * 1000 / 90);
>                 //switch_core_timer_next(&timer);
>                 ts += wait;
>             }
>
>             if (switch_channel_test_flag(channel, CF_VIDEO) && ts >=
> videoNext)
>
>             {
>                 switch_byte_t *data = (switch_byte_t *) vid_frame.packet;
>
>                 vid_frame.data = data + 12;
>                 vid_frame.datalen = vid_frame.packetlen - 12;
>                 switch_core_session_write_video_frame(session, &vid_frame,
> SWITCH_IO_FLAG_NONE, 0);
>                 videoSent = true;
>             }
>
>             if(aOk && ts >= audioNext)
>
>             {
>                 if (write_frame.datalen > (int) write_frame.buflen)
>                     write_frame.datalen = write_frame.buflen;
>
>                 switch_core_session_write_frame(session, &write_frame,
> SWITCH_IO_FLAG_NONE, 0);
>                 audioSent = true;
>                 audioNext += 90000 / 50; // 20ms
>             }
>         }
>
>     Btw, thanks for the tip. I'll keep the separate thread to store video
> for the record function.
>
>     Regards,
>
>     Paulo
>
>
> On 13/07/10 15:39, Anthony Minessale wrote:
>
> we need to get nonblocking reads to the rtp working so the
>
>   read_video_frame();
>    read_audio_frame();
>
>  don't block when there is no data.
>
>
>
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>


-- 
Anthony Minessale II

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