[libav-bugs] [Bug 281] New: avconv: Rate control broken for mpegvideo based encoders

bugzilla-daemon at aruru.libav.org bugzilla-daemon at aruru.libav.org
Fri May 4 20:21:15 CEST 2012


           Summary: avconv: Rate control broken for mpegvideo based
           Product: Libav
           Version: git HEAD
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: Normal
         Component: general
        AssignedTo: bugzilla at libav.org
        ReportedBy: martin at martin.st

The following commit broke rate control for mpegvideo based encoders (libx264
seems to be fine):

commit 832ba44d8d91d5c5ad47843085f810bde74a2e6d
Author: Anton Khirnov <anton at khirnov.net>
Date:   Tue Feb 7 11:03:33 2012 +0100

    avconv: saner output video timebase.

    r_frame_rate should in theory have something to do with input framerate,
    but in practice it is often made up from thin air by lavf. So unless we
    are targeting a constant output framerate, it's better to just use input
    stream timebase.

To reproduce, do something like this:

./avconv  -i <any flv file> -an -vcodec flv -vb 1000k -y test.flv

In most cases, the actual output bitrate will be much lower than the desired
one. This happens most probably since the codec expects the frame rate set by
the codec time base, aiming at way too few bits per frame.

One potential solution would be to fix the rate control to take the frame
timestamps into account.

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