[mythtv] h264 recordings showing double length - counting fields rather than frames?

[Mark Buechler]

Nobody with h264 expertise has any thoughts on this? This issue effects all
interlaced h264 content.

- Mark.

On Mon, May 12, 2008 at 2:01 PM, Mark Buechler <mark.buechler at gmail.com>
wrote:

> Yes, another "double length" thread. This time I think the problem is a bit
> different.
>
> I have several channels all coded in h264 interlaced. MythTV shows these
> recordings as being double length. In poking around, I found that in
> DTVRecorder::FindH264Keyframes(), _frames_seen_count is incrementing double
> what it should (~60) given the content is only 30 fps. It was suggested on
> #mythtv that we're counting fields rather than frames here.
>
> So next I poked around in mpeg/h264utils.cpp in
> KeyframeSequencer::KeyframePredicate() and looked at the h264 spec and found
> that NAL type SEI should tell us whether or not the content is interlaced. I
> don't know if parsing each SLICE NAL is what's required here or simply
> looking at the ct_type in the SEI to determine if the stream is interlaced
> and, if it is, skip every other SLICE (sounds hackish).
>
> I'm really not familiar with h264 so I'm looking for suggestions and/or
> sample code or maybe a sanity check on what I've found.
>
> Thanks, Mark.
>
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