H.264快速重新编码

Question

I'm working on a (sort of a) VOIP application for mobile with video support. Most of modern smartphones are equipped with hardware H.264 encoder/decoder. However most of those support only a limited number of encoding profiles. In particular I'm interested in SVC, which is not supported usually. The simplest solution would be to use a software encoder. But, obviously, it has its drawback.

Recently an idea came to me to create a hybrid hardware+software encoder. Which consists of a hardware encoder, and a "shallow software recoder".

I know (in very general terms) that H.264 works in term of a macroblocks. The encoded stream contains instructions for macroblocks: either full retransmit (in a form of jpeg-like data), its motion parameters, or just nothing.

A full software recoding would process such an encoded stream, parse/realize it, and execute on its image data, then encode the resulting image, which includes processing each macroblock, decision on strategy, building motion vectors, and, finally, encoding all the instructions.

The idea is to do a "shallow" recoding. I though about parsing an incoming encoded stream, but instead of executing its instructions - just use them as a source for encoder, ie encode them within H.264 sophisticated encoding scheme, with the needed precision (ie bitrate) and etc, without actually analyzing the image, finding motion vectors and etc.

In essense, it's using decoder+encoder, but with a shortcut, so that the actual image is not created by the decoder, and not analyzed by the encoder.

Does this sounds feasible? Was there an attempt to do something similar?

Answer 1

I don't think it's feasible to do. I've heard similar suggestions from people with basic understanding of video encoding without clear knowledge of actual h264 encoding. It might be possible but that would take prohibitively long time to achieve any sensible results. You could for example contract some of the best developers from x264 and that would perhaps cost you around 100K to get any results. Your best bet to validate my answer is to ask x264 or ffmpeg maligning list.