stuart wrote: > However, I couldn't get the sound and video on the MVPMC to sync up. It > appeared to be somewhere between a second and a faction of a second off. > After jumping around it looked better, but never right on. I played > back the same recording with mythfrontend and the recording and audio > were synchronized from the get go and jumping around didn't change that. >... > So, what's the difference between this transcoded recording and a > recording off my OTA NTSC tuner (which plays back perfectly on my MVPMC > box)?
My theory is that mvpmc is not doing true synchronization, and thus it is more susceptible to offsets in the way the audio and video are mutiplexed into the stream. See this message from the developer list: http://www.nabble.com/Re%3A-Audio-Sync-problems-workaround-p12759212.html where the author of the recent audio sync fixes explains why, despite the audio packets being "tagged with time code," the mvpmc software isn't able to fully utilize that information to enforce sync. I believe if we could obtain better documentation of the media playback hardware in the MVP, this problem could be resolved properly. > Any help as to what we might do to tweak it is appreciated. Given this, I believe mencoder supports options for offsetting the audio and video streams, and toying with those options might permit dialing in the sync on the MVP. Though it is likely that the offset will be different for each combination of video and audio bitrates. A lower-level examination of the multiplexed media stream might permit a more automated solution, where say the audio bitrate is artificially boosted to keep pace with the video. Using constant bitrate encodings for both the audio and video might also help. (I forget which is which, but MPEG2 is probably CBR already, and I believe MP3 is as well.) > This go around is comparing a good (video/audio in sync) OTA NTSC file > w/a OTA ATSC HDTV w/2.1 AC3 file that has been transcoded using Roger's > script. [...] > The differences in the files are: > problem recording (remember: OTA NTSC): > VIDEO: MPEG2 640x480 (aspect 1) 29.970 fps 5924.0 kbps (740.5 kbyte/s) > > good recording (remember: OTA ATSC HDTV w/1.2 AC3 -> transcoded): > VIDEO: MPEG2 480x480 (aspect 2) 29.970 fps 6000.0 kbps (750.0 kbyte/s) Don't you have your "problem" and "good" labels backwards? They seem to be contradictory to your earlier statement. > The transcoded file appears to have sync problems everywhere > except when using mythfontend (i.e. mplayer). Technically, I believe mythfontend uses different libraries/code than mplayer. I believe its player is built on the ffmpeg libraries. I bet your problem video would likely playback fine with other software decoders as well. > 6) And something about the audio bit rate I don't understand: > > problem recording: > AUDIO: 48000 Hz, 2 ch, s16le, 160.0 kbit/10.42% (ratio: 20000->192000) > ID_AUDIO_BITRATE=160000 > > good recording: > AUDIO: 48000 Hz, 2 ch, s16le, 384.0 kbit/25.00% (ratio: 48000->192000) > ID_AUDIO_BITRATE=384000 What's the part you don't understand? The first, processed with Roger's script, had the audio set to 160 kbit/s by the script. (The audio bitrate is hard coded at a fixed value, as noted earlier in this thread.) The latter apparently was recorded with 384 kbit/s. Roger Heflin wrote: > I did not always have audio sync issues, I started having the sync > issues when I changed the MythTV bitrate, before that > everything appeared to work correctly. After changing the bitrate the > audio tended to be out of sync some of the time even though testing > with mythfrontend and mplayer showed that the audio was perfectly > in sync. That's exactly what I experienced. Sync was generally quite good until I dropped my MythTV recording bitrates (and resolutions) to save on disk space. > This has gotten alot better with the new mvpmc version... Likewise, as noted on the developer list. > ...but it appears to me that bitrate has some bearing on the audio > being in sync or not. Agreed. -Tom ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Mvpmc-users mailing list Mvpmc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mvpmc-users mvpmc wiki: http://mvpmc.wikispaces.com/
