CAVLC -> CABAC?

omion · 26th December 2005, 08:43

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?

akupenguin · 26th December 2005, 08:59

There is no such tool existing, but it shouldn't be hard to write.

Chainmax · 26th December 2005, 16:03

Forgive my complete and utter ignorance, but it can be done in a lossless way? How?

Sharktooth · 26th December 2005, 16:18

Converting CABAC compressed data in CAVLC... something like converting a 7-zip archive into a normal zip.

virus · 26th December 2005, 16:23

Quote:

Originally Posted by Chainmax

Forgive my complete and utter ingorance, but it can be done in a lossless way? How?

Entropy coding via CABAC or CAVLC is done as last step, after ME and quantization have taken place. Let's say it's a lossless process that just "writes down to the bitstream" the already-computed data (transformed&quantized coefficients, macroblock types, motion vectors, plus additional side-infos). All you need to do is to decode the CAVLC/CABAC stream and reencode it to the other format, while signalling in the slice headers that you've switched entropy coder type. Nothing will be lost in the process, since detail removal (which comes from quantization) need not be performed again. You just redo the very last step in your encoding chain (see what I've written above).

Chainmax · 26th December 2005, 17:07

So, it would be akin to switching headers on a video stream or demuxing and remuxing into a different container?

omion · 26th December 2005, 20:43

@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.

j7n · 8th August 2006, 09:26

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?

Limobar · 8th August 2006, 10:15

I would welcome a CABAC-to-CAVLC-converter because that would make more encodes decodable for the Xbox.

codimahi · 8th August 2006, 10:32

Quote:

Originally Posted by j7n

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?

Conversion from CABAC to CAVLC includes CABAC decoding and CAVLC encoding in which both are very computational intensive. Let's say for a 1hr h.264 CABAC encoded movie, this recompression may take more than 3hrs(depend on resoulution). I don't think so any body would like to do this before seeing a very interesting movie.

j7n · 8th August 2006, 10:38

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

check · 8th August 2006, 12:19

Quote:

Originally Posted by omion

@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.

Slightly off topic - I'm assuming you use VMR to view subtitles. However, MPC's internal subtitle renderer uses VMR7 (which is faster), and vsfilter runs best in overlay, so why use VMR9?

akupenguin · 8th August 2006, 17:15

Quote:

Originally Posted by codimahi

Conversion from CABAC to CAVLC includes CABAC decoding and CAVLC encoding in which both are very computational intensive. Let's say for a 1hr h.264 CABAC encoded movie, this recompression may take more than 3hrs(depend on resoulution). I don't think so any body would like to do this before seeing a very interesting movie.

No. CABAC is about 20-40% of the decoding time (depending on bitrate). CAVLC is less. If you can play the CAVLC version in realtime (otherwise you wouldn't be converting), then the CABAC version can't be more than 30% slower than realtime.
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.

Inventive Software · 8th August 2006, 17:37

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?

sysKin · 9th August 2006, 04:20

Quote:

Originally Posted by Inventive Software

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?

CABAC/CAVLC is THE two ways of writing a bitstream

Quote:

Does CAVLC happen anyway even if CABAC is enabled?

No, it's one or the other.

Limobar · 14th October 2006, 02:01

Quote:

Originally Posted by akupenguin

There is no such tool existing, but it shouldn't be hard to write.

Quote:

Originally Posted by akupenguin

I'd expect the converter to run no slower than 1.5x realtime.

Dear Developers,

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

pokazene_maslo · 16th September 2009, 18:48

I second this request. It would be a useful tool for users with slower machines.

iwod · 17th September 2009, 10:07

Does this tools exist after nearly 3 years?

Shevach · 17th September 2009, 14:19

Quote:

Originally Posted by akupenguin

CABAC is about 20-40% of the decoding time .

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.

roozhou · 17th September 2009, 15:25

Could someone write a CABAC <-> CAVLC bitstream filter for ffmpeg?

26th December 2005, 08:43	#1 \| Link
omion Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 325	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? __________________ "We demand rigidly defined areas of doubt and uncertainty!" - Vroomfondel, H2G2

26th December 2005, 08:59	#2 \| Link
akupenguin x264 developer Join Date: Sep 2004 Posts: 2,392	There is no such tool existing, but it shouldn't be hard to write. Last edited by akupenguin; 26th December 2005 at 09:01.

26th December 2005, 16:03	#3 \| Link
Chainmax Huh? Join Date: Sep 2003 Location: Uruguay Posts: 3,103	Forgive my complete and utter ignorance, but it can be done in a lossless way? How? __________________ 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
Sharktooth Mr. Sandman Join Date: Sep 2003 Location: Haddonfield, IL Posts: 11,768	Converting CABAC compressed data in CAVLC... something like converting a 7-zip archive into a normal zip. __________________ MPEG-4 ASP Custom Matrices: EQM V1(old), EQM AutoGK Sharpmatrix (aka EQM V2), EQM V3HR (updated 01/10/2004), EQM V3LR, EQM V3ULR (updated 04/02/2005), EQM V3UHR (updated 17/12/2004) and EQM V3EHR (updated 05/10/2004) Info about my ASP matrices. MPEG-4 AVC Custom Matrices: EQM AVC-HR Info about my AVC matrices My x264 builds. Mooo!!!

26th December 2005, 17:07	#6 \| Link
Chainmax Huh? Join Date: Sep 2003 Location: Uruguay Posts: 3,103	So, it would be akin to switching headers on a video stream or demuxing and remuxing into a different container? __________________ 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.

26th December 2005, 20:43	#7 \| Link
omion Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 325	@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. __________________ "We demand rigidly defined areas of doubt and uncertainty!" - Vroomfondel, H2G2

8th August 2006, 09:26	#8 \| Link
j7n Registered User Join Date: Apr 2006 Posts: 137	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?

8th August 2006, 10:15	#9 \| Link
Limobar aka Rabomil Join Date: Sep 2005 Posts: 82	I would welcome a CABAC-to-CAVLC-converter because that would make more encodes decodable for the Xbox.

8th August 2006, 10:38	#11 \| Link
j7n Registered User Join Date: Apr 2006 Posts: 137	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, 17:37	#14 \| Link
Inventive Software Turkey Machine Join Date: Jan 2005 Location: Lowestoft, UK (but visit lots of places with bribes [beer]) Posts: 1,953	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? __________________ On Discworld it is clearly recognized that million-to-one chances happen 9 times out of 10. If the hero did not overcome huge odds, what would be the point? Terry Pratchett - The Science Of Discworld

16th September 2009, 18:48	#17 \| Link
pokazene_maslo Registered User Join Date: Apr 2009 Location: Martin, Slovakia Posts: 79	I second this request. It would be a useful tool for users with slower machines.

17th September 2009, 10:07	#18 \| Link
iwod Registered User Join Date: Apr 2002 Posts: 756	Does this tools exist after nearly 3 years?

17th September 2009, 15:25	#20 \| Link
roozhou Registered User Join Date: Apr 2008 Posts: 1,181	Could someone write a CABAC <-> CAVLC bitstream filter for ffmpeg? Last edited by roozhou; 17th September 2009 at 15:35.

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