Comment 7 for bug 436726

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Oibaf (oibaf) wrote : Re: Please sync libtheora 1.1.0-1 from debian (unstable)

Hi Jean-François, thanks for the test. You should note at least two things:

1) theora 1.0 was not able to meet the selected birate when using -v option. From http://www.theora.org/news/#libtheora-1.1.0:
"The new rate control module hits its target much more accurately and obeys strict buffer constraints, including dropping frames if necessary. The latter is needed to enable live streaming without disconnecting users or pausing to buffer during sudden motion. Obeying these constraints can yield substantially worse quality than the 1.0 encoder, whose rate control did not obey any such constraints, and often landed only in the vague neighborhood of the desired rate target. The new --soft-target option can relax a few of these constraints, ..."

This mean the the worse quality with 1.1 and -v option is a "feature" and not a "bug". Indeed with 1.0 when you selected -v 500 or -v 1000 the bitrate was almost the same: the encoder was not able to use the 500Kbps bitrate.

You can check the real bitrate with "ogginfo". Of your encoding:
1.0 -v500 is using a 1344,850909 kb/s Average bitrate --> much higher that the 500 requested
1.1 -v500 is using a 561,485643 kb/s Average bitrate --> very similar to the 500 requested

1.0 -v1000 is using a 1411,508464 kb/s Average bitrate --> much higher that the 1000 requested
1.1 -v1000 is using a 997,679248 kb/s Average bitrate --> very similar to the 1000 requested

2) When using the 1.1 theora the -V meaning has changed. You can't compare two files encoded with the same -V value, but you should change the -V value up to getting similar bitrate (or you could use the --two-pass option).

Also remember that the -v option should only be used when you want to get a file with a constant bitrate (e.g. for video streaming over Internet). For best quality you should use -V.

So it would be nice if you can redo the -V test changing the -V value up to getting a similar size.