What does the video bitrate (currently at 5000000) do?
Should I tinker with it?
My Humax Forum » Freeview HD » Aura UHD
Aura Download file size.
(33 posts)-
| Thu 11 Feb 2021 13:47:10 #21 |
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Note the file Video Bitrate and the actual video bitrate
Attachments
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50_fps_File_and_Video_Bitrates.jpg (143.3 KB, 2 downloads) 3 years old
| Thu 11 Feb 2021 13:56:55 #22 | -
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Showing Adjacent Frames in videoredo and single frame exported as .jpg
Attachments
- Single_Frame_as_.jpg (67.9 KB, 1 downloads) 3 years old
- Adjacent_Frames_In_Videoredo.jpg (160.4 KB, 1 downloads) 3 years old
| Thu 11 Feb 2021 14:07:01 #23 | -
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I think I've demonstrated that the extra frames don't take up (materially) more space. A 50fps version of a 25fps source will (through the encoding algorithm) effectively say "Frame 1 - ABCDEFGHIJ", "Frame 2 - as Frame 1", "Frame 3 - EFGHJILK", "Frame 4 - as Frame 1" so it is much more effectively compressed.
Point taking about the 1080i HD broadcasts, that was casual laziness on my part.
Anyway, the point is that you can control the frame rate and bitrate from the WebControl page and you can conrol bitrate only from the Aura itself.
Changing the framerate between 50 and 25 doesn't make a material difference to file size (at least, not in the programme I tested) though as noted the 25fps is faster to encode (I just tested that).
| Thu 11 Feb 2021 14:33:20 #24 | -
grahamlthompson - 39 mins ago »
Note the file Video Bitrate and the actual video bitrate
Not sure what changing the transcoding bitrate should have on final filesize.
However the average Bitrate used by a BBC1-HD recording is about 7000kbps.
Assuming 8 bits to a byte (ignoring extra parity bits) Over 1 hr that that should create a file of about 3GB.
So that's close to the start file size before you reduce each 1920 x 1080 frame to 720 x 576 plxels. That's about a 20% reduction for each frame. 3 x 0.8 = 2.4GB
Very close to the filesize shown in the screen grab from Videoredo.
If you look at the file analysis it clearly says frame doubled. That doesnt mean its recompressing one frame and the doing it again. It simply means that once a frame is compressed it adds a second copy of the same frame thus doubling the apparent frame rate. If you look carefully at the Videoredo screen shot,
you can clearly see you get two adjacent identical frames with this repeated for the next frame. Interpolating two adjacent frames to create a new frame based on difference between the two is very processor intensive especially on the fly.| Thu 11 Feb 2021 14:44:43 #25 | -
There is one way I can show this. IF export jpeg images from adjacent frames. Pen them in Photoshop.
Add a new layer under the frame 1 image. Copy the frame 2 image to the lower layer any then reduce top layer opacity so you can see the underlying frame any differences should be clearly visible.
| Thu 11 Feb 2021 15:14:11 #26 | -
Yes, but modern compression / encoding uses algorithms to keep file sizes small and efficient. I know I'm over-simplifying the process but a duplicated frame doesn't take the same space on the disc that the initial frame does, far from it. Anyway, i think I've demonstrated that the 50fps files are not significantly larger than the 25fps files, no matter how they do it.
I agree Frame 2 will be a duplicate of Frame 1 in a 50fps output from a 25fps source (normally); but it doesn't mean that Frame 2 takes the same space within the file because that's the way the various encoding / compression algorithms work.
| Thu 11 Feb 2021 15:45:30 #27 | -
larkim - 11 mins ago »
Yes, but modern compression / encoding uses algorithms to keep file sizes small and efficient. I know I'm over-simplifying the process but a duplicated frame doesn't take the same space on the disc that the initial frame does, far from it. Anyway, i think I've demonstrated that the 50fps files are not significantly larger than the 25fps files, no matter how they do it.
I agree Frame 2 will be a duplicate of Frame 1 in a 50fps output from a 25fps source (normally); but it doesn't mean that Frame 2 takes the same space within the file because that's the way the various encoding / compression algorithms work.That's clearly wrong. The original HD video is compressed using H264/AVC AKA AVC.
The downloaded file also uses H264/AVC. There is no way the aura is recoding each frame using H264/AVC. It has to taking each Group of pictures as is.
A GOP contains one Iframe (the only one with a full image) with the rest containing lossy difference data. The H264/AVC decoder in the device playing back the video stream recreates the whole number of frames in the GOP. It can only do this for a complete GOP.
Video redo can be set to only jump from Iframe to Iframe. So you can jump from onr GOP to the next.
| Thu 11 Feb 2021 16:09:06 #28 | -
Just tried a larger file (30 minutes) and same result. 25fps file 526Mb, 50fps file 535Mb.
I'm now wondering though if that is more because I'm not halving the bitrate despite halving the framerate.
Confusing myself... !
| Thu 11 Feb 2021 16:20:35 #29 | -
larkim - 4 mins ago »
Just tried a larger file (30 minutes) and same result. 25fps file 526Mb, 50fps file 535Mb.
I'm now wondering though if that is more because I'm not halving the bitrate despite halving the framerate.
Confusing myself... !The average total bitrate and the duration of the recording are directly related to the final size of the file.
The Video track will of course be larger than the audio ones
Basically how much smaller does the 50fps file get if you recode it to 25fps using something like Vidcoder. You can retain the resolution and change the framerate in vidcoder.
Attachments
- Reduce_Framerate_Retain_resolution.jpg (72.2 KB, 1 downloads) 3 years old
- H264_encoding_25_fps.jpg (88.3 KB, 1 downloads) 3 years old
| Thu 11 Feb 2021 16:37:00 #30 | -
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