BBC HD on DVB-S dropped video frames. [ Not in mplayer/vnc ]

[anonymous]

I am seeing dropped frames in mythtv while playing back BBC HD-TV. this is an h.264 MBAFF stream, so has fairly heavy cpu requirements. I can play these streams back cleanly on the same machine under windows, and using vlc/mplayer. Looking at mythfrontend -v playback, frames are being dropped because the audio is 3 frames out of step with the video. Increasing the tolerance on this with a quick hack does not solve the problem. I am run tests on current SVN, using both FFMPEG (h264) and with the coreavc patch to give me more headroom on the cpu.

Originally posted to mythtv-users.

PC is core2duo e4300 [overclocked], graphics card nvidia 7300Ls. Cpu 
load is recorded as {cpu core0:core1} 

Windows2000: 
2.7GHz : VLC: ffmpeg: no skiploopfilter: BBC-HD MBAFF h.264: CPU 60%:20% smooth. 
2.7GHz : VLC: ffmpeg: skiploopfilter: BBC-HD MBAFF h.264: CPU 40%:10% smooth. 
2.7GHz : MplayerClassic: coreavc: no skiploopfilter: BBC-HD MBAFF h.264: CPU 60%:30% smooth. 
2.7GHz : MplayerClassic: coreavc: skiploopfilter: BBC-HD MBAFF h.264: CPU 40%:20% smooth. 

Ubuntu 7.04. . 

2.7GHz : VLC: ffmpeg: no skiploopfilter: BBC-HD MBAFF h.264: CPU 100%:20% and dropped frames. 
2.7GHz : VLC: ffmpeg: skiploopfilter: BBC-HD MBAFF h.264: CPUs 90%:20% smooth. 
2.7GHz : Mythtv: ffmpeg: skiploopfilter: BBC-HD MBAFF h.264: CPU 90%:20% and dropped frames. 
2.7GHz : Mythtv: coreavc: skiploopfilter: BBC-HD MBAFF h.264: CPU 40%:40% and dropped frames. 

So it looks as if I can reduce the quality of the ffmpeg decoding by 
using skiploopfilter to not max out the CPU, or use a non-free coreavc 
codec. However Mythtv is still doing somthing odd with the Sync between 
Audio and Video which is leading to it detecting the audio falling out 
of sync with the video, and then dropping video frames to resync. 

[john]

OK, Just by accident I was running another program which tied up the sound card. With no sound the video playback is perfectly smooth in mythtv. The problem must be to do with sync / detected audio parameters in mythtv. [mute has no effect]

[john]

Tactical Solution:

As I could play these recordings in vlc, I tried using vlc to remux (NOT TRANSCODE) a sample clip. Using vlc this way I can remux the streams, replace the original stream, rebuild the seek table, and play back using the myth internal player, without frame drop.

I have a tactical solution now, using vlc/mythcommflag --rebuild as a user job to remux the video, so I can watch it in Mythtv.

I would be more than happy to provide any further information to get to the bottom of this problem.

[anonymous]

The continuous dropped frames has been fixed by the latest ffmpeg sync r13655.

Please close.

[Stuart Auchterlonie]

Closing as requested. Fixed by [13655], the ffmpeg resync