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26th December 2005, 08:43 | #1 | Link |
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CAVLC -> CABAC?
I've just started to encode an HDTV movie, and have been playing around with the settings. After a few quick tests, I found that at 720p24 I can't play back CABAC-encoded files, but I can play CAVLC. Is there any tool available which can "recompress" between the two?
My idea is to encode with CAVLC and just accept the slightly larger file until I get my next computer. Then I'll "recompress" the file to CABAC to save space. So is there anything available which can do this? If not, is it something simple enough to expect it to be available in the future?
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26th December 2005, 16:03 | #3 | Link |
Huh?
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Forgive my complete and utter ignorance, but it can be done in a lossless way? How?
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Read Decomb's readmes and tutorials, the IVTC tutorial and the capture guide in order to learn about combing and how to deal with it. Last edited by Chainmax; 26th December 2005 at 17:05. |
26th December 2005, 16:18 | #4 | Link |
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Converting CABAC compressed data in CAVLC... something like converting a 7-zip archive into a normal zip.
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26th December 2005, 16:23 | #5 | Link | |
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26th December 2005, 17:07 | #6 | Link |
Huh?
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So, it would be akin to switching headers on a video stream or demuxing and remuxing into a different container?
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26th December 2005, 20:43 | #7 | Link |
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@Chainmax:
It would be a bit like changing containers, but Sharktooth's zip analogy is better. The data is compressed with either CABAC or CAVLC before it is written to a file. By the way, I found I can read 720p24 CABAC movies as long as I use the overlay mixer. Since I watch a lot of subbed anime, I always have VMR9 renderless on, but it seems to be a bit too slow in this case.
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8th August 2006, 09:26 | #8 | Link |
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As far as I understand CABAC considerably increases CPU load during playback. I think that after recompressing into CAVLC my older computer would be able to decode my H.264 files in real-time. Has the situation changed after 7 months and a tool to convert between CABAC & CAVLC become available?
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8th August 2006, 10:32 | #10 | Link | |
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8th August 2006, 10:38 | #11 | Link |
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However computation intesive or unoptimized that program might be it would really help if purchasing a faster computer (or re-encoding the video) is not an option.
The choice is real simple: *- spend 3hrs and watch the movie *- do not watch the movie at all Last edited by j7n; 8th August 2006 at 10:41. |
8th August 2006, 12:19 | #12 | Link | |
phjbdpcrjlj2sb3h
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8th August 2006, 17:15 | #13 | Link | |
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But the CABAC->CAVLC converter doesn't have to do any of the other steps of decoding, it just parses the bitstream and writes it out again. So at the high end (CABAC=40% of decoding, CAVLC version takes 100% CPU), I'd expect the converter to run no slower than 1.5x realtime. |
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8th August 2006, 17:37 | #14 | Link |
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Potentially stupid question, but I'll ask anyway.
Does the CABAC/CAVLC take place in each frame after the ME and bitstream has been written? Or is it done before the bitstream is written? Or is it done completely different? EDIT: Does CAVLC happen anyway even if CABAC is enabled?
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9th August 2006, 04:20 | #15 | Link | ||
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14th October 2006, 02:01 | #16 | Link | ||
aka Rabomil
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Please consider writing a tool that converts CABAC to CAVLC. People that use the Xbox (XBMC) would then be able to enjoy so much more content that is available, but not decodable because of the limited processing power of the Xbox and the processing power needed by CABAC. The combination of a tool that appears not to be that hard to write (according to akupenguin) and the reasonable conversion time needed, in my opinion, makes it worth the effort. I hope you feel the same. Regards, Limobar |
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17th September 2009, 14:19 | #19 | Link |
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In average CABAC performance is 20-40% higher than CAVLC one. But CABAC encoding/decoding can have severe performance peaks (unlike CAVLC where peaks are significantly smaller).
The reason is that CABAC is very hard for optimization due to back-dependency between bins. Choice of context models for some bins depends on the values of previous bins (e.g. the bins of mb_type). So, CABAC can not easely pipelined. Some encoders deliberately switch to CAVLC mode when performance peak in CABAC encoding/decoding expected. Thus a smart CABAC->CAVLC converter should switch to CAVLC only if video content might cause performance peak. |
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