Re: H.264 Profile and Level

Hey Jason,

On Wed, Sep 15, 2010 at 11:42 AM, Jason Tackaberry <[email protected]> wrote:
> Although, is parsing the output of mkvinfo an option for your use-case?
> I didn't know mkvinfo would dump codec private data.

Not exactly ;o)  mkvinfo gave me most of what I needed by default.
For the codec private data, however, I had to run mkvinfo -v -v -v,
which reports offsets for fields.  I was able to combine a few offsets
to locate the private data, after which I could do a simple read of
the relevant bytes in python.  It felt messy enough that I started to
look for an alternative and found kaa.metadata.

On another note, I wrote to the author of mkvinfo when I was working
on that approach, and he added the level (and maybe the profile) to
the codec private line of the output.  I haven't tried it yet, as I
had switched to kaa before he added the feature.  I use mkvinfo a lot
though, and will download the new version to try it out shortly.

> I could imagine other scenarios where having access to the profile and
> level would be useful.  I might want to expose these as video track
> attributes.  Would you mind sharing the code you're using to parse this
> out?

It's pretty minimal, but seems to work correctly:

    meta = kaa.metadata.parse(source)
    [stuff]

    # i is the video track number
    (h264_profile, h264_level) = struct.unpack_from('>HB',
meta.video[i].codec_private_id[1:4])

The profile is encoded as follows:
    0x42E0 - Baseline Profile
    0x4D40 - Main Profile
    0x58A0 - Extended Profile
    0x6400 - High Profile

And to get the level you just divide by 10 (e.g. 0x1f = 31, 31/10 = level 3.1).

> Yes, I've meanwhile added 'codec_private' as core attributes for video
> and audio tracks, which is initialized to None when not present, or a
> string of bytes when it is.
>
> Thanks for the submission!

Excellent - thanks very much!

Mike.

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