[x264-devel] Generating H264 for iPad?

[Hadmut Danisch]

Hi,

I just ran into a particular problem with ffmpeg and H264 encoding, and
was forwarded by package maintainers to this mailing list.


I'd like to convert several videos into H264, most of them into
1280x720, currently testing bitrates between 700k and 2000k. I'd like to
use the generated videos on Computers, network DLNA streamers, and
mobile devices such as iPad.

The problem I've ran into:

The videos I generate with ffmpeg (e.g. ffmpeg -i sample_in.mp4 -vcodec
libx264 -vpre superfast -b 2000k -acodec copy -s 1280x720 -aspect 16:9
sample_out.mp4 ) can be viewed without any problem on computers and my
network streamers, but not on my iPad. The iPad drops frames, can't
generate full screens, completely freezes the screen. This does not
happen if I reduze the resolution. The problem is obviously that the
iPad does not have enough computation power.

Interestingly, I have other videos downloaded from Internet (e.g.
youtube) which have the same resolution (H264, 1280x720, around
2000kb/s)  which are displayed smoothly and without any problem on the
iPad.

>From what I've learned about H.264, several mobile devices including
iPad do have hardware decoders, which are not able to decode every
possible flavor of H264 encoding, only some. I guess that problem is
that videos generated with libx264 are not compatible with iPad's
hardware decoding, thus require the CPU, which is overloaded.


The question:

Does anyone know how to use libx264 to generate H264 videos that run
smoothly and with hardware decoding on mobile devices?



regards
Hadmut