compression artifacts in video and bitrates

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markyboy81 Veteran Member • Posts: 4,319
compression artifacts in video and bitrates

I shot some video of my family in fairly heavy snowfall yesterday - it was 4k 25fps at 80mbps HEVC.

Usually when I edit the video (only making minor adjustments and combining clips) I find that if I output to around 14mbps QHD using the h264 codec (unfortunately no HEVC available) the result is pretty good with no artifacts.

I'm wondering if the snowfall somehow caused the low bitrate to not be able to cope as there were lots of artifacts in my son's face at the 14mpbs bitrate? I tried increasing it and it improved a little bit at 30mpbs but still nowhere near the original.

Could the snowfall have caused these issues? There were also some issues with the autofocus as I guess the big flakes of snow confused the system. Are there any other scenarios to be aware of when considering what bitrate to output the video to? I know fast movement is one, wondered whether there were any others.

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Lee Jay Forum Pro • Posts: 56,673
Re: compression artifacts in video and bitrates
1

markyboy81 wrote:

I shot some video of my family in fairly heavy snowfall yesterday - it was 4k 25fps at 80mbps HEVC.

Usually when I edit the video (only making minor adjustments and combining clips) I find that if I output to around 14mbps QHD using the h264 codec (unfortunately no HEVC available) the result is pretty good with no artifacts.

I'm wondering if the snowfall somehow caused the low bitrate to not be able to cope as there were lots of artifacts in my son's face at the 14mpbs bitrate?

Absolutely.

I tried increasing it and it improved a little bit at 30mpbs but still nowhere near the original.

Could the snowfall have caused these issues?

Yes.

There were also some issues with the autofocus as I guess the big flakes of snow confused the system. Are there any other scenarios to be aware of when considering what bitrate to output the video to? I know fast movement is one, wondered whether there were any others.

The bit rate you need to faithfully reproduce video is *incredibly* sensitive to how much change there is between frames in the video.  Mostly static - 3Mbps might be enough.  Very noisy and lots of motion - 80Mbps might not be enough.

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OP markyboy81 Veteran Member • Posts: 4,319
Re: compression artifacts in video and bitrates

Thanks Lee, that's helpful to know.

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onlyfreeman
onlyfreeman Senior Member • Posts: 2,405
Re: compression artifacts in video and bitrates

I'm no expert with video and I don't know what software you are using, but I hear sometimes a 2-pass encoding could really help with this kind of issue, unless I'm mistaken. Is your software capable of that?

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OP markyboy81 Veteran Member • Posts: 4,319
Re: compression artifacts in video and bitrates

onlyfreeman wrote:

I'm no expert with video and I don't know what software you are using, but I hear sometimes a 2-pass encoding could really help with this kind of issue, unless I'm mistaken. Is your software capable of that?

Good point, I've heard about 2-pass encoding from using Handbrake, but I've never really understood how it works.

Unfortunately the app I use doesn't support this, but I guess an option could be to use the app to output a high bitrate, and then convert it again using 2-pass encoding in Handbrake or similar.

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John Sheehy Forum Pro • Posts: 24,341
Re: compression artifacts in video and bitrates

markyboy81 wrote:

onlyfreeman wrote:

I'm no expert with video and I don't know what software you are using, but I hear sometimes a 2-pass encoding could really help with this kind of issue, unless I'm mistaken. Is your software capable of that?

Good point, I've heard about 2-pass encoding from using Handbrake, but I've never really understood how it works.

Unfortunately the app I use doesn't support this, but I guess an option could be to use the app to output a high bitrate, and then convert it again using 2-pass encoding in Handbrake or similar.

You could start by shooting "All-I" if your card speed and capacity can handle it, then take a 4 or 5 second slice of the video, and convert it to different bitrates and compression options, if you actually need to, to see what the maximum practical compression would be.

Why 25fps, I wonder?  Are monitors in "PAL" territory these days still doing 25 and 50Hz?  I assumed that for digital, computer-driven video, 30Hz, and 60Hz are more standard, globally.

NickZ2016 Senior Member • Posts: 1,796
Re: compression artifacts in video and bitrates

John Sheehy wrote:

Why 25fps, I wonder? Are monitors in "PAL" territory these days still doing 25 and 50Hz? I assumed that for digital, computer-driven video, 30Hz, and 60Hz are more standard, globally.

Monitors maybe but lights still flicker . Not an issue outdoors in sunlight but most people aren't going to do outdoors at 30 and indoors at 25.

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OP markyboy81 Veteran Member • Posts: 4,319
Re: compression artifacts in video and bitrates

John Sheehy wrote:

markyboy81 wrote:

onlyfreeman wrote:

I'm no expert with video and I don't know what software you are using, but I hear sometimes a 2-pass encoding could really help with this kind of issue, unless I'm mistaken. Is your software capable of that?

Good point, I've heard about 2-pass encoding from using Handbrake, but I've never really understood how it works.

Unfortunately the app I use doesn't support this, but I guess an option could be to use the app to output a high bitrate, and then convert it again using 2-pass encoding in Handbrake or similar.

You could start by shooting "All-I" if your card speed and capacity can handle it, then take a 4 or 5 second slice of the video, and convert it to different bitrates and compression options, if you actually need to, to see what the maximum practical compression would be.

Why 25fps, I wonder? Are monitors in "PAL" territory these days still doing 25 and 50Hz? I assumed that for digital, computer-driven video, 30Hz, and 60Hz are more standard, globally.

I shoot 25fps due to the flickering that I would experience shooting under artificial light at 30fps.

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John Sheehy Forum Pro • Posts: 24,341
Re: compression artifacts in video and bitrates

NickZ2016 wrote:

John Sheehy wrote:

Why 25fps, I wonder? Are monitors in "PAL" territory these days still doing 25 and 50Hz? I assumed that for digital, computer-driven video, 30Hz, and 60Hz are more standard, globally.

Monitors maybe but lights still flicker . Not an issue outdoors in sunlight but most people aren't going to do outdoors at 30 and indoors at 25.

Good point, but there are less and less lights that use the power mains for timing these days.  It is good to be aware of the light source qualities.

OP markyboy81 Veteran Member • Posts: 4,319
Re: compression artifacts in video and bitrates

John Sheehy wrote:

NickZ2016 wrote:

John Sheehy wrote:

Why 25fps, I wonder? Are monitors in "PAL" territory these days still doing 25 and 50Hz? I assumed that for digital, computer-driven video, 30Hz, and 60Hz are more standard, globally.

Monitors maybe but lights still flicker . Not an issue outdoors in sunlight but most people aren't going to do outdoors at 30 and indoors at 25.

Good point, but there are less and less lights that use the power mains for timing these days. It is good to be aware of the light source qualities.

That's true. At the same time I can't really see much difference between 25fps and 30fps. And with the lower frame rate and the same bitrate the quality has the potential to be better (although possibly not noticeably)

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