Help with understanding bit rates

[james b norman]

so, the new GH4 offers 4K video at 100mbps, and offers 1080p at 100mbps. I think that means that the 4k footage is being way more compressed than the 1080 footage - is that correct?

also, if the footage is being recorded at 100mbps, the file sizes for both 4k and 1080 would be the same - is that correct?

and lastly, if the file sizes are the same, why does it require such a much more powerful computer to render the 4k footage than the 1080 footage?

thanks.

 

[jkoch2]

so, the new GH4 offers 4K video at 100mbps, and offers 1080p at 100mbps. I think that means that the 4k footage is being way more compressed than the 1080 footage - is that correct?

Only an intrepid few will ever bother to shoot 1080p at 100mbps. It might improve the quality of slow-mo, but only if the light is very good too.

The GH4 also allows 1080p capture at 50mbps or lower settings. An extra 50mbps won't make the cats look any feline. After compression to 5mbps for YouTube or phone video, they all look like motley alley cats.

also, if the footage is being recorded at 100mbps, the file sizes for both 4k and 1080 would be the same - is that correct?

Yes, provided the codecs are the same. I don't know if XAVC-S is more compact than MOV with the same bitrates. Ultimately, h.265 HEVC could make everything smaller, but this will be a delivery, not a capture, codec.

and lastly, if the file sizes are the same, why does it require such a much more powerful computer to render the 4k footage than the 1080 footage?

Probably dependent on the graphics card requirement to support a 4k array, which might simply not exist in older or simpler cards. It takes lots of processor power and time to render (and compress) any large files.

Android tablets with Tegra-2 processors cannot play even AVCHD files.

thanks.

--
jnorman
sunridge studios
salem, oregon
Panasonic GH4, Vario 7-14mm f/4
Cambo 45NX, nikkor SW 90/8, 135/5.6, 210/5.6
Graflex Crown Graphic 4x5 (1948 model)

 

[Victor Engel]

so, the new GH4 offers 4K video at 100mbps, and offers 1080p at 100mbps. I think that means that the 4k footage is being way more compressed than the 1080 footage - is that correct?

also, if the footage is being recorded at 100mbps, the file sizes for both 4k and 1080 would be the same - is that correct?

and lastly, if the file sizes are the same, why does it require such a much more powerful computer to render the 4k footage than the 1080 footage?

thanks.

 

[Lab D]

so, the new GH4 offers 4K video at 100mbps, and offers 1080p at 100mbps. I think that means that the 4k footage is being way more compressed than the 1080 footage - is that correct?

Only an intrepid few will ever bother to shoot 1080p at 100mbps. It might improve the quality of slow-mo, but only if the light is very good too.

It is not for everyone, but the GH4 can also do 1080p at 200Mbps. This is very popular with the independent film makers. It is near lossless video and allows for a wider range of editing.

 

[JJ Rodin]

so, the new GH4 offers 4K video at 100mbps, and offers 1080p at 100mbps. I think that means that the 4k footage is being way more compressed than the 1080 footage - is that correct?

also, if the footage is being recorded at 100mbps, the file sizes for both 4k and 1080 would be the same - is that correct?

and lastly, if the file sizes are the same, why does it require such a much more powerful computer to render the 4k footage than the 1080 footage?

thanks.

--
jnorman
sunridge studios
salem, oregon
Panasonic GH4, Vario 7-14mm f/4
Cambo 45NX, nikkor SW 90/8, 135/5.6, 210/5.6
Graflex Crown Graphic 4x5 (1948 model)

My question to you is what is the encoder (codec) being used for 4k and 2k ?

If 4k is being compressed via the H.265 (new) encoder, while the 2k is being encoding using older H.264 encoder, then the resulting compression comparison may be more complicated that just numbers.

The H.265 is MUCH more efficient to encode, takes more h/w to encode & playback, much like mp2 vs mp4 playback. If decoding is done in h/w not CPU, a lesser issue.

4k is being encoded with 10bits, 422 subsampling, H.264 is 8bit, 420 subsampling, so which is the larger file - I would think 4k, 20% larger or more.

Playback of 4k is purely dependent on your graphics card, unless quite new, will NOT be used for 4k H.265 decoding, thus CPU usage will be large !! The CPU will be using software decoder I assume or graphics card might help in the decoding - not likely I think.

Generally, the higher the bit rate for Capture is desirable, then you decrease that after editing and for final product.

PS: ALL compression via any codec is NOT the same, some implimentations of codecs are better than others, sometimes hugely !! Just like JPEG renderings from raw.

Enjoy that GH4!

 

[JJ Rodin]

so, the new GH4 offers 4K video at 100mbps, and offers 1080p at 100mbps. I think that means that the 4k footage is being way more compressed than the 1080 footage - is that correct?

Only an intrepid few will ever bother to shoot 1080p at 100mbps. It might improve the quality of slow-mo, but only if the light is very good too.

It is not for everyone, but the GH4 can also do 1080p at 200Mbps. This is very popular with the independent film makers. It is near lossless video and allows for a wider range of editing.

That would only be much better if the subsampling is 422 &/or 10bit H.264, vs std H.264. 10bit DR is much better + 422, a much better 2k video!!

 

[Lab D]

so, the new GH4 offers 4K video at 100mbps, and offers 1080p at 100mbps. I think that means that the 4k footage is being way more compressed than the 1080 footage - is that correct?

Only an intrepid few will ever bother to shoot 1080p at 100mbps. It might improve the quality of slow-mo, but only if the light is very good too.

It is not for everyone, but the GH4 can also do 1080p at 200Mbps. This is very popular with the independent film makers. It is near lossless video and allows for a wider range of editing.

That would only be much better if the subsampling is 422 &/or 10bit H.264, vs std H.264. 10bit DR is much better + 422, a much better 2k video!!

GH4 supports both 10 bit and 422 output to an external recorder. I am told the high bit rate allows for sharper details, especially if there is movement or scenes with things like green trees, and allows for more flexibility in color grading and such.

The big argument right now is over if 4K 4:2:0, 8 bit can really convert to 1080P 4:4:4 10 bit like several experts claim.

 

[LingoDingo]

The H.265 is MUCH more efficient to encode, takes more h/w to encode & playback, much like mp2 vs mp4 playback. If decoding is done in h/w not CPU, a lesser issue.

I haven't seen any video camera able to encode with the new h.265 CODEC, which I suspect is largely the result of the much higher processing power required by this CODEC. It will come eventually, but I doubt we will see anything in a camera this year.

The Panasonic GH4 enables several different encoding formats ( AVCHD, MP4, MOV ) that are either some variation of h.264 encoding or ALL-I frame encoding.

With GH4 4K footage, the recommended CODEC is h.264 100 Mbps IPB format using either an MP4 or MOV file container to hold your data. IPB is a variable bit-rate format that maxes out at 100 Mbps on the GH4.

If file size is an issue for you, then you can choose 1080p AVCHD at 24 Mbps, or the equivalent h.264 MP4 format. This records a good image, but not the best the camera can produce. The higher bit-rates are for maximum image quality.

For 1080p footage you can also choose 100 Mbps IPB format or up to 200 Mbps ALL-I format. ALL-I format is best used for high speed image changes, like fast pans, zooms, or when filming a fast changing subject.

 

[Sean Nelson]

With GH4 4K footage, the recommended CODEC is h.264 100 Mbps IPB format using either an MP4 or MOV file container to hold your data. IPB is a variable bit-rate format that maxes out at 100 Mbps on the GH4.

This isn't a higher data rate per pixel than the GH3 is capable of, but it's pretty much equivalent to the standard 28Mbit/sec 1080p AVCHD standard. And when you consider that most people won't be watching 4K video on a display that's twice as big (i.e., 100" screen vs. 50"), that means that any artifacts will be less noticeable because they'll appear smaller.

 

[LingoDingo]

With GH4 4K footage, the recommended CODEC is h.264 100 Mbps IPB format using either an MP4 or MOV file container to hold your data. IPB is a variable bit-rate format that maxes out at 100 Mbps on the GH4.

This isn't a higher data rate per pixel than the GH3 is capable of, but it's pretty much equivalent to the standard 28Mbit/sec 1080p AVCHD standard. And when you consider that most people won't be watching 4K video on a display that's twice as big (i.e., 100" screen vs. 50"), that means that any artifacts will be less noticeable because they'll appear smaller.

I'm still waiting for somebody to do a proper comparison between the 8-bit 4K 4:2:0 internal footage and 10-bit 4K 4:2:2 externally recorded footage.

I'm already in love with the internal footage, so the 10-bit external might take things to a whole other level...

 

[JJ Rodin]

With GH4 4K footage, the recommended CODEC is h.264 100 Mbps IPB format using either an MP4 or MOV file container to hold your data. IPB is a variable bit-rate format that maxes out at 100 Mbps on the GH4.

This isn't a higher data rate per pixel than the GH3 is capable of, but it's pretty much equivalent to the standard 28Mbit/sec 1080p AVCHD standard. And when you consider that most people won't be watching 4K video on a display that's twice as big (i.e., 100" screen vs. 50"), that means that any artifacts will be less noticeable because they'll appear smaller.

I'm still waiting for somebody to do a proper comparison between the 8-bit 4K 4:2:0 internal footage and 10-bit 4K 4:2:2 externally recorded footage.

I'm already in love with the internal footage, so the 10-bit external might take things to a whole other level...

As well as compare to the new 4k BM cam. 100mbs is quite low especially for 4k, raw would be so MUCH higher for 4k - 10x or more.

The encoders (IQ & sizes) will be very interesting to watch, internal - external of GH4 and other encoding of 4k raw.

Interesting times !!

 

[LingoDingo]

100mbs is quite low especially for 4k, raw would be so MUCH higher for 4k - 10x or more.

It's equivalent to shooting 1080 HD at 24 Mbps, but with the higher resolution you won't notice defects as easily as 1080 footage.

The encoders (IQ & sizes) will be very interesting to watch, internal - external of GH4 and other encoding of 4k raw.

4K RAW recording requires very expensive gear, with the sole exception being the Blackmagic 4K Production camera. Affordable 4K recording will get here eventually, but I think we've still got a couple of years to go before that happens. ( the $2,000 Atomos Shogun will be one of the first, and this price is still in the prosumer price range )