zuloogolf.blogg.se - Setting process priority freac

#Setting process priority freac download

Frames might require more reservoir than is available after joining with frames coming from other codec instances.

After dealing with the above, frames need to be put back into an MP3 compatible bitstream after joining.

Frames are not available in discrete form, but may be overlapping each other.

The encoder might not return all encoded frames after processing a chunk of data as some frames might still be waiting for additional data to put in the bit reservoir.

When dealing with MP3, multiple issues arise from the peculiarities around the bit reservoir:

Pass next chunk of audio to worker thread.

Check if worker thread has encoded frames.

Find next worker thread and wait until it is ready.

The SuperFast encoding loop usually looks like this (click to jump to example source code): This requires the frames to be available in discrete form in order to deal with overlap and joining the frames correctly. SuperFast works by passing chunks of audio data to separate encoder instances and later joining the encoded data blocks back together in the right order. So this is a problem when implementing the SuperFast technology for MP3. In real world MP3 streams, the situation can be even more intricate.

Here the frame headers come after the data and in case of frame #5, there even is data of another frame (#6) between its data and its header. Looking at only the 5th and 6th frame, their layout in the bitstream looks like this: It even leaves some space, so the first data block of the 6th frame starts in the 4th frame as well. The 5th frame is only one data block long and that data block fits completely into the 4th frame. This space available to following frames is called bit reservoir and allows the codec to maintain a set target quality in most cases, even when frame sizes are fixed and audio complexity changes. In an MP3 bitstream, however, (at least for CBR files, VBR is more complicated) frames have a fixed size and when there is space left in a frame after all samples have been encoded, that space can be used by the following frames. In an AAC bitstream, each frame will simply have a length matching the number of data blocks required for that frame and the frames will neatly come one after another. The individual frame lengths are 4, 3, 4, 3, 1, 5, 5 and 7 blocks. In this example, the average frame size is 4 blocks of data. The main difficulty is that while most other formats have discrete frames of audio samples in their bitstreams, MP3 frames can overlap each other: SuperFast LAME is significantly more complex than the SuperFast components for AAC, Opus and Speex, mostly because of technical peculiarities of the MP3 format.

#Setting process priority freac download

You can download a preview release of fre:ac with SuperFast LAME support from GitHub. Tl dr: Implementing SuperFast LAME required some additional work to handle certain features of the MP3 format. So I finished the SuperFast LAME multi-threaded MP3 encoder last week and it's time to write about some technical aspects of it.