GNOME Bugzilla – Bug 644919
avenc_mpeg2video: Default bitrate too low
Last modified: 2018-11-03 12:55:27 UTC
I was trying to create a video DVD VOB file with ffmux_dvd. The only video encoder listed for that container is ffenc_mpeg2video. The default bitrate is only 300000, which gives a very blocky appearance with poor resolution, especially in darker parts of the image. A more reasonable value of 6548000, which I found somewhere on the "Interwebs", maintains the quality of the original file, and also yields an approximately correct file size for the length of the DVD. I started with an ordinary NTSC DVD, with 480x360 resolution. Preferred behavior would be for PiTiVi not to degrade the quality of the input files by default. If that's too difficult, an acceptable way to fix the problem would be just to choose a correct value for normal DVD quality. A word about the severity. Although this should be a simple problem to fix, I'm marking the severity as "major", because it always yields poor quality output for DVDs. The average user (me) is already overwhelmed by the huge number of options and parameters, while simultaneously troubleshooting multiple problems with video software.
Potentially a bigger gstreamer issue with defaults in general.
There is nothing to be done on the pitivi side because - we do not override the defaults, we get the values as is from gstreamer - there is no universal bitrate that would work for every use case: bitrate depends on the complexity/amount of movement, on resolution, framerate, etc. Leaving open to see if something can be done on the gstreamer side, but I'm not sure about that. See also bug 118142
Thanks for commenting over there. I notice that it's been 8 years since that gstreamer bug was reported. I understand the stated Pitivi philosophy of moving bugs upstream and not creating specific patches for Pitivi, but the usefulness of that approach depends on bugs getting patched upstream. Unfortunately, this one is not getting patched. My best suggestion is to fix it with a kludge if necessary, and if that's too hard for some reason I can't imagine, at least document it clearly so users can deal with it. To give you an idea of the severity, as I recall this cost me all my evenings for a week of troubleshooting, posting to unhelpful support Web sites, trying many other programs (which also failed for various uninteresting reasons), and reading lots and lots of unspecific, aimless documentation. In alternate universes (i.e. competing OS's), my understanding is that one can just use the default video editor without problem. I sympathize, though. Video standards are a mess. A comment in the plan reads, "Read it and weep".
Let's resolve this as NOTABUG, there's no good default for every use case. Applications or users should set whatever bitrate makes sense for them.
I'm not sure I agree. We should have somewhat sensible defaults for our encoders, at least for 'major' formats like MPEG-2 video. Could be done in set_format based on the input resolution, for example if libav doesn't provide a better way. If our defaults are bad, people will just blame GStreamer for outputting bad quality by default.
*** Bug 645157 has been marked as a duplicate of this bug. ***
-- GitLab Migration Automatic Message -- This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity. You can subscribe and participate further through the new bug through this link to our GitLab instance: https://gitlab.freedesktop.org/gstreamer/gst-libav/issues/5.