tomlee59
Member
Joined: 26 Aug 2005
Location: Palo Alto, California USA
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First, my apologies, Major, for a negative-sounding post, but that's tough to avoid when reporting bugs. I do sincerely appreciate the tremendous effort you have obviously put into developing ffmpegX. That said...
I use ffmpegX almost exclusively for encoding movies into KVCD/XVCD format, for playback on old Macs and PCs that lack a DVD drive, and which lack the CPU horsepower for DivX. I imagine that I'm about the only human left who cares a whit about VCDs, so likely these requests will shoot straight to the bottom of your "to do" list, just below "clean tile grout."
At least up to ffmpegX 0.0.9v, analysis of the source DVD characteristics seems not to be as thorough as it could be. As a result, conversion into KVCD ends up a very hit-or-miss affair. Simple movies, like The Princess Bride, convert without a hitch. Others, like Galaxy Quest, can be fixed with a little cutting and splicing (mpeg2enc gets confused by two scene breaks which cause jumps in sync errors; at least the post-break rates are ok, so just cutting, demuxing, realigning, remuxing and recombining the three segments will solve the problem, but it's more work than should be necessary). Many more, like The Right Stuff, exhibit the traditional problem of an ever-worsening time misalignment. It does not appear to be a simple pulldown-related problem (setting/clearing the pulldown flag does not solve the problem). Rather, it appears from analyzing the info log output that the source is dynamically altering frame rates (or mpeg2enc thinks this is happening) and ffmpegX (or the underlying analysis tool that is responsible for tracking this) can't keep up. As I understand it, this is a known problem with mpeg2enc. Scene changes with several black frames in between seem to cause particular problems. I can fix linearly changing sync with an audio post-processing step, but it would be nice not to have to do so. Or at minimum, it would be nice if there were some analysis of the source that could flag in advance that a sync problem will occur. Then the user could avoid wasting time on a conversion that is doomed to fail.
Is there any hope of getting the folks who work on mpeg2enc to fix this, er, feature? In the meantime, shifting to a Windows machine and running EazyVCD is the minimum-fuss alternative...
Other bugs/requests:
1) Aspect ratio often chosen incorrectly. It's not a big deal to choose the right parameters manually, but it would be nice to have this done automatically.
2) Movie duration often reported incorrectly (seems to default to 91 minutes when it can't figure it out), throwing off calculations of correct bit rate. I always double-check the original DVD source for correct duration. If this bug can't be fixed, eliminate the feature (at minimum, inform the user "unable to determine correct duration" so that we know when we need to check it independently). For now, I treat "91 minutes" as equivalent to "Check duration" (of course, occasionally, I do run into a movie that *is* actually 91 minutes in duration).
3) For XVCDs, ffmpegx frequently aborts while muxing ("too many dropped frames" or some such thing is often reported in the info log), leaving the elementary streams and the aborted mpg behind. But if I use the muxing tool by itself, I can always mux the elementary streams with no trouble. This is puzzling; perhaps the script is muxing as VCD, rather than as XVCD?
4) For true VCDs, elementary streams are not kept, even if I click on "save elementary streams." The exception is that they are kept only if muxing fails.
5) Unclicking "encode video" or "encode audio" by itself does not disable encoding. Passthrough must also be selected. These really should be coupled together, or at least a message of some sort should be passed to the user if one only deselects "encode." A user will naturally expect disabling encode to mean that encoding will not occur.
6) Encoding just the audio track of a DVD does not seem possible at present, at least, not from a VIDEO_TS folder. If I merge the VOB files (using D-Vision), ffmpegX can handle encoding just the audio from that fine. I assume this limitation is due to some legal issues related to the DMCA, but if not, it would be nice to permit it.
7) Over-writing of files is too easily done with this tool. Is it hard to add a quick check to see if it's about to over-write some files, and then pop up a dialog box if it does? It's disheartening to lose a bunch of work over such a simple thing. Software should not only work for us, it should help prevent us from doing bonehead things. 
--Cheers,
Tom
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