Is VDR _really_ the only solution to sync problems?

schmibble said:

Thanks, moyekj. That both answers my question and explains why Tivo can afford to take such a cavalier attitude toward the sync issue. All right, I'll grit my teeth and do V-redo.

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I don't believe this is TiVo. All the box does is wrap the mpeg2 transport stream into its TiVo wrapper as-is without doing any real transcoding. It's the broadcasters who create the HD transport streams and - likely even more problematic - the cable companies trying to shoehorn as much "HD" content into their bandwidth limited coaxial cable with as much compression as they think they can get away with; compare OTA with same program from cable frame by frame some time. It's dramatic - I call it "horrid definition" - and broadcasters are also severely compressing some programming, live sports is one very noticeable example. I've little doubt the TS timestamping problem, and the audio sync issue it creates, is a direct result of this.

Furthermore the BCs and cable providers have zero motive to clean it up as long as it "plays" reasonably in sync. That someone might want to record and archive programs is not their problem, indeed anything that hampers this serves their content DRM and protection interest. My cable company is doing added compression of the transport streams, but no further transcoding that I can discern. Content differs between channels depending on how the cable company receives it. Some are 720p, supposedly 59.94 fps and some are 1080i allegedly at 29.97 fps. In reality I've found the mpeg2 frame rates vary within the stream and that 1080i is often a mix of interlaced and progressive. Not certain about 3:2 pull down for telecine of cinema but would not be surprised if that's sloppy too.

As already cited, decoders are much more robust to this in realtime playback for display on a screen, but the sloppy timestamping with varying frame rates and mix of interlaced containing some progressive frames completely fouls up some encoders. It results in stuttering video and/or audio gradually slipping out of sync. I, like others, have found VideoRedo marvelous for editing TiVo HD recordings from cable without creating sync problems or stuttering video. It's also been able to repair stuttering video in many mpeg2s after a simple transcode with another tool like NeroVision has induced it (yes, even with Smart Encoding doing as-is frame copying). Doesn't help with creating Blu-Ray discs though as NeroVision frequently regenerates choppy stuttering video from 1080i recordings even with its Smart Encoding being used.

I've had good results with maintaining 720p as 720p at 59.94 fps, and 1280x720 59.94 fps progressive mpeg2 is a legit Blu-Ray format. Have also had good results transcoding some problematic 1080i/29.97 fps to 720p/59.94 fps, or to 1080p/23.976 fps. I'll take a 10 minute or so sample and try each to see which works best, the latter usually working very well with cinema (movies) that were originally shot at 24fps. Note that 1080p - progressive - at 23.976 fps is also a legit Blu-Ray mpeg2 format. None of these transcoding transformations take very long with a reasonable speed dual-core processor; no more than 2-3 hours for a 2-1/2 hour movie. I don't recommend transcoding the TiVo mpeg2 into H.264 AVC mp4 for 720p/60, 1080p/24 or 1080i/30 Blu-Ray for practical reasons. While H.264 AVC is a superior compression scheme that can pack greater resolution into smaller storage space, it's also much more computationally complex, which means it can take days to transcode a 1080i/29.97 mpeg2 into a 1080i/29.97 H.264 AVC mp4 versus taking a few hours to transcode into a comparable mpeg2. OTOH, transcoding to an appropriate H.264 (there are at least 10 "flavors" of H.264) for devices like an iPod Touch, an iPhone or even an iPad is another matter, and usually doesn't take all that long as the output is much smaller resolution for a portable device screen versus HD resolution Blu-Ray.

Finding some strategies that worked for me was quite time consuming and frustrating. YMMV with specific versions of Nero. I have 8 and 10, and the transcoding codecs in them are different. Fortunately I can also have both versions installed simultaneously without problems. Sometimes I've found one better than the other for transcoding a specific recording to the same Blu-Ray format.

John

jcthorne said:

I was with you and agreed with most every thing you posted up to this point. With a current processor it certianly does NOT take DAYS to encode a 1080p24 h264 video from an mpg2 original. On my laptop with an I7 Quad core at 2.2Ghz which is by no means bleading edge, just corporate issue mainstream these days, 1080p24 video encodes in just a bit longer than real time. IE about 3 hrs for a 2 hr film. But then again, file size drops from 20+ GB to about 6 for nearly identicle video quality and a file that can push to tivo in MUCH faster than real time, usually only a few minutes.

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What are you using to do the transcoding? My efforts at AVC transcoding have met with outrageous times required using a 3.3 GHz AMD x6 1100T.

In further experiments, EncoreHD in particular (movie channel on cable) streams all their movies in 1080i at 29.97fps, apparently using a telecine pulldown scheme to get 30fps from 24fps cinema. Causes major video stuttering issues with NeroVision (in Nero 8 and 10) trying to maintain it in 1080i at 29.97 fps. I've come to the conclusion it's most likely an inability to maintain the telecine pulldown properly. Still experimenting some with 1080p at 23.976 fps and 720p at 59.4 fps. While the stuttering video does not occur with 1080p at 23.976 fps, audio gradually slips out of sync. By the end of a 2 hour movie it's rather noticeable. 720p at 59.94 fps also avoids stuttering video and keeps audio in sync. Would like to find a way to use 1080p @ 23.976 fps though. NeroVision is very finicky with allowing SmartEncoding to frame copy the video stream.