My filming goals, Bitrate vs framerate vs compression? (tl;dr warning)

[Roman]

Hey guys,

First of all I'd just like to say that if not for Magic Lantern, I'd have not bought a DSLR.

I had in mind that if I was going to spend $$$$ (comparatively) on a camera, it would need a minimum amount of features such as timelapse, which none seem to have out of the box... Found Magic Lantern, bought a 600D and life has been grand 

Okay, so one thing that I want to acheive this year, is to make a good quality video about taking my racecar to the track, racing around, the social side of it, etc. As well as a timelapse or two and a few of Magic Lanterns other fun features.

My plan so far is to record with:

600D with 8mm Samyang fisheye lense, stereo shotgun mic.
This will be mounted in the car looking out the windscreen / view of driver, will record at 720p 60fps.

Netbook with a 20hz GPS receiver and software, a webcam connected recording at 640x480 30fps for a picture in picture view of perhaps the pedals/drivers feet.
The audio portion of the webcam video will be with a Blue Yeti USB mic in a secondary position to capture engine noise, or exhaust noise or whatever.

A Contour HD modified to recieve an external mic input, this could possibly use the headphones output of the Yeti mic as the input, or put the shotgun mic on this and use the standard Canon audio.

So I'm pretty much sorted for what I want to do with the above I guess, but there are some other segments I am planning to shoot where I am torn between aiming for 1080p or 720p.

Since there's a maximum bitrate for the camera (is this before or after compression?) is there any picture quality to be gained by shooting at say 720p 24fps over 1080p 24fps? Would less colour detail etc get compressed down by the codec, if more data can be allocated to each frame? Or is it not likely to make a difference?

Since some portion of the video will be 720p anyway to get 60fps, I figure I'll aim for this for the rest, if it's a case of post codec quality advantage vs pixel count.

If anyone can help, or perhaps has any hints or tips for shooting in car / out of car automotive stuff, I would greatly appreciate it

[Roman]

One other question, since the audio portion presumably consumes part of the available video bitrate, would disabling sound where not required, give a better quality picture also?

(Theoretically at least... my filming skills are likely the bottleneck for now!)

[Malcolm Debono]

Sounds like a good plan

For scenes were you don't intent to do slo-mo in post, I suggest shooting in 1080p24. I also wanted to remind you that there is no 720p24. It's either 720p50 or 720p60 (depending if your camera is set to PAL or NTSC).

If you're not using the audio track, you can disable it, which in turn allows you to increase the video bitrate (through ML) further while remaining quite stable. However, do experiment with how high you can go since this depends on a number of factors including the scene, ISO, audio, card specifications, etc.

[Roman]

Okay thanks.

I thought you could adjust the framerate with magic lantern, independant of what the original options were now?

Or does that mean 60fps changed to 24fps in ML will play back as fast forward? (Havent tried yet)

[JasonATL]

Before shooting something serious with 720p on the 600D, I strongly suggest experimenting and seeing for yourself whether you are happy with the image you get. My own opinion is that the moire and aliasing is so much worse in 720p mode that I have stayed away from it. I do not think that the 600D does a very good job at downscaling to 720p. This is not something that ML can improve on (I wish they could).

Malcolm has given very good advice. If you need the best video quality (and don't need sound), you can disable audio and turn up CBR in 1080 24p mode. I've had very good success on the 600D using up to about 2.0x CBR with audio disabled. If the camera can't take it, then just dial CBR back until it doesn't stop automatically. I've found 1.4x works usually even with sound.

[1%]

This will be mounted in the car looking out the windscreen / view of driver, will record at 720p 60fps

rrrrrrrrRolling shutter.


1080p skips lines... .720p skips more lines. The max you'll get is 80-100MBps and video looks really "clear" like that.


You have a pretty wide lens, you can try crop mode... I don't think it does any line skipping, but you lose shallow DOF.

[Roman]

Yep, although cmos wobble is an issue with the rolling shutter, based on some thoroughly unscientific testing it apprears  to be a lot less an issue than with other HD cameras I've played with. (like gopro / contourhd)

Presumably because the 600D scans each line at a quicker rate / more processing power?

Does minimising the shutter speed help with that issue at all?

I've done a few in car tests with it (just street driving though) and no noticable CMOS wobble.

The webcam that I've got connected gets it horribly, which is why I'll have it pointed at something relatively stationary. (Like the foot pedals)

[Datadogie]

Always video at the highest 1080p when you can. As it's much better to downsize than upsize. Therefore only use 50/60fps if you intend to use slow motion.