H264 level limitation in WATCHOUT 6.2

[Miro]

H264 level limitation in WATCHOUT 6.2

Hi, the updated H264 decoder in WATCHOUT 6.2 has a level 5.2 limitation. It’s a third-party codec not developed by Dataton so this limitation is outside of our control. The codec update was necessary to eliminate important bugs. This level limitation shouldn’t really be a big problem for most users since most video editing tools have the same level 5.2 limitation in their encoder. In more extreme scenarios where huge and odd resolutions are required this may be a problem but there are workarounds!

 

Each level in H.264 is basically a combination of constraints like the maximum number of luma samples per second and the maximum number of macroblocks per second. The number of luma samples equals the number pixels and a macroblock is 16x16 pixels.

 

In level 5.2 the maximum number of pixels per second equals 530 841 600. For example:

• A DCI 4k footage at 60 frames per second: 4096 x 2160 x 60 = 530 841 600 luma samples/s which is exactly at the limit.
• A super wide video for a custom LED wall at 60 Hz: 8192 x 1024 x 60 = 503 316 480 luma samples/s is slightly below the limit.

Videos with a higher luma count will be encoded using a higher level then 5.2 and will not be rendered in WATCHOUT 6.2!

The easiest workaround would be to export the video as HAP or HAPQ but in some cases the large file size of HAPs causes problems when it comes to distribution of the files from a remote producer over internet.

 

Some encoders like x264 can be forced to use a certain level despite of the luma count. You will get a bunch of warnings, but it doesn’t stop the encoding process. In WATCHOUT the decoder checks only the level of the video and if it’s lower or equal then 5.2 it will play even if it’s an 8k60 video.

For example, you can use ffmpeg to transcode an 8k (7680 x 4320@60fps) video with a forced level:

 

ffmpeg -i input.mp4 -c:v libx264 -refs 2 -level 5.2 -profile:v high -pix_fmt yuv420p -g 30 -bf 0 -b:v 200M output.mp4

 

And this video will play successfully in WATCHOUT if your CPU is powerful enough. 

 

//Miro