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I need a simple and fast video codec with alpha support as an alternative to Quicktime Animation which has horrible compression rates for regular video.

Since I haven't found any good open-source encoder/decoder with alpha support, I have been trying to write my own (with inspiration from huff-yuv).

My strategy is the following:

  1. Convert to YUVA420
  2. Subtract current frame from previous (no need for key-frames).
  3. Huffman encode the result from the previous step. Split each frame into 64x64 blocks and create a new huffman table for each block and encode it.

With this strategy I achieve decent compression rate 60-80%. I could probably improve the compression rate by splitting each frame into block after step 1 and add motion vectors to the reduce the data output from step 2. However, better compression-rate than 60% is lower prio than performance.

Acceptable compression-speed on a quad-core cpu 60ms/frame.

However the decoding speed suffers, 40ms/frame (barely real-time with full cpu usage).

My question is whether there is a way to compress video with much faster decoding, while still achieving decent compression rate?

Decoding huffman-coded symbols seems rather slow. I have not tried to use table-lookups yet, not sure if table lookups is a good idea since I have a new huffman table for each block, and building the lookup-table is quite expensive. As far as I have been able to figure out its not possible to make use of any SIMD or GPU features. Is there any alternative? Note that it doesn't have to be lossless.

ronag
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You want to try a Golomb Code instead of a Huffman Code. A golomb code is IMO faster to decode then a huffman code. If it doesn't have to be loseless you want to use a hilbert curve and a DCT and then a Golomb Code. You want to subdivide the frames with a space-filling curve. IMO a continous subdivision of a frame with a sfc and also a decode is very fast.

Micromega
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