Hey Jason,
On Wed, Sep 15, 2010 at 11:42 AM, Jason Tackaberry <t...@urandom.ca> 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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