[FFmpeg-user] A/V sync problems with h264/aac video fragment

Andy Sheen sheen.andy at googlemail.com
Mon Apr 16 17:27:41 CEST 2012

Konrad Karl wrote on Mon 16 Apr at 16:09 UK time
> Hi,
> On Mon, Apr 16, 2012 at 03:47:10PM +0100, Andy Sheen wrote:
>> Konrad Karl wrote on Mon 16 Apr at 15:32 UK time
>> If you want to make something playable by almost any hardware that does
>> H.264 acceleration, you should limit yourself to BluRay profile which is
>> H.264 High Profile/Level 4.1. The Taj scene is High Profile/Level 4.2
>> which is why there are problems.
> It is not my goal to have i play everywhere but some of my relatives
> and me have WD TV Live boxes and it should play there.

These only support H.264 at 1080p24. See below.

> Having seen the panning smoothness of p50 I really dont want to go to p24.
> I know there are people who like the old fashioned cinema look....

WD Live boxes won't guarantee to play this. This is what the product
spec says:

* MPEG2 MP at HL up to 1920x1080p24, 1920x1080i30 or 1280x720p60
* MPEG4.2 ASP at L5 up to 1280x720p30 resolution and no support for global
  motion compensation.
* WMV9/VC-1 MP at HL up to 1280x720p60 or 1920x1080p24 resolution. VC-1
  AP at L3 up to 1920x1080i30, 1920x1080p24 or 1280x720p60 resolution.
* H.264 BP at L3 up to 720x480p30 or 720x576p25 resolution.
* H.264 MP at L4.1 and HP at 4.1 up to 1920x1080p24, 1920x1080i30, or
  1280x720p60 resolution.

Basically, if you want your 1080p50 source material to guarantee to
play, you will either have to convert to 1080i50, framerate convert to
1080p24 or resize to 720p50.

All of these chips have been developed for broadcast apps where the
bandwidth isn't typically used to broadcast 1080p50. It is normally
1080i50. BluRay added the 1080p24 and as that's about the same
complexity as 1080i50, the chipsets support them. Most streamed data
(i.e. ripped BluRays) doesn't go beyond 1080p24, hence why it isn't
supported on the cheaper consumer streamers.

>>> The elephant scene has not that much movement detail and I really 
>>> want to know what exactly is generating so much work at the decoder.
>> The encoding profile.
> I would want to dig deeper into the level of detail because this
> problem has made me quite curious (decode speed going down from 
> ~1.1 to 0.7 but just on that 30 second sequence within the whole movie)

It isn't "work at the decoder" that is causing the problem - but the
fact that as you are encoding at HiP at L4.2 just means you are pushing it
beyond what it is designed to do. You may well find a set of settings
that work for this file, but the next encode may not work with the same
set of settings. If you want best motion, record at 1080p50, encode to
720p50. If you want best picture clarity, record/encode at 1080p24.


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