[libav-bugs] [Bug 541] New: MPEG4 video profile not set in get_format()

bugzilla at libav.org bugzilla at libav.org
Wed Jul 17 18:58:50 CEST 2013


https://bugzilla.libav.org/show_bug.cgi?id=541

           Summary: MPEG4 video profile not set in get_format()
           Product: Libav
           Version: git HEAD
          Platform: X86
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: libavcodec
        AssignedTo: bugzilla at libav.org
        ReportedBy: remi at remlab.net


libavcodec fills in the profile and level information for MPEG4 part 2 video
tracks only after the get_format() context callback is invoked.

For hardware acceleration to work nicely, the application needs to check that
the hardware supports the profile and level. In particular, only SP and ASP are
usually supported for MPEG4 part 2. So the application needs to know the
profile and level at the time get_format() gets called.

For H.264/AVC, this works fine.

Unfortunately, there is no way (that I'd know) to test hwaccel within libav.
This can however be tested with recent VLC from git:

# vlc --avcodec-hw dummy -vv big_buck_bunny_480p_surround-fix.avi
...
[0xaca0f5a0] main generic debug: looking for hw decoder module matching
"dummy": 2 candidates
[0xaca0f5a0] hwdummy generic debug: codec 13 (mp4v) profile -1 level -1
[0xaca0f5a0] main generic debug: using hw decoder module "hwdummy"
[0xacae4768] avcodec decoder debug: Available decoder output format 109 (vdpau)
[0xacae4768] avcodec decoder: Using Dummy video decoding accelerator for
hardware decoding.
[0xacae4768] avcodec decoder debug: avcodec codec (MPEG-4 Video) started
[0xacae4768] main decoder debug: using decoder module "avcodec"
...

Note the line with "profile -1 level -1". By comparison, with H.264:

[0xb66e6b58] main generic debug: looking for hw decoder module matching
"dummy": 2 candidates
[0xb66e6b58] hwdummy generic debug: codec 28 (h264) profile 77 level 30
[0xb66e6b58] main generic debug: using hw decoder module "hwdummy"
[0xabc6e7e8] avcodec decoder debug: Available decoder output format 109 (vdpau)
[0xabc6e7e8] avcodec decoder: Using Dummy video decoding accelerator for
hardware decoding.

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