[x264-devel] Different pic_init_qp_minus26 cause stitching to fail.

[Anders Rein]

Hi,

I am working on a software which transcodes clips and commercial to 
different resolution and serve the correct content to various media 
devices. We've been using x264 via ffmpeg for encoding h264. Recently we 
updated x264 from snapshot-20120705 to snapshot-20130303. This caused 
our stitching of commercial and video content to fail.

The stitching fails because the pic_init_qp_minus26 in the 
picture_parameter_set differs between the clips. The results vary from 
foggy and saturate results to complete crash (depending on the decoder).

Re-encoding is not an option since content needs to be stitched on the 
fly. I made a remuxer that changed the PPS/SPS Id before stitching, but 
only a hand full of the players tested supported multiple SPS/PPS in a 
video (ffplay and android go, iphone and vlc no).

I was wondering if maybe it would be a good idea to allow to manually 
set the pic_init_qp_minus26 via a parameter? What is the gain from 
setting the pic_init_qp_minus26 value closer to the average qp? fewer 
bits in the delta_qs value?

By the way, we use mp4 as container and use MP4Box (part of gpac) to 
stitch videos.

Anders Rein