Magic Lantern tackles the video bitrate on the Canon EOS 5D Mark II

by planetmitch1 Comment

The Magic Lantern Canon EOS 5D Mark II firmware has a new beta release allowing higher bitrates in video – all the way up to 74 Mbps. We first learned about this several days ago when it was posted by Scott in this planet5D forum thread and we've been doing some research about the details before bringing you this post. We'd rather give you the most info we can to help you understand why this is significant.

Redrock Micro

Canon settings

When Canon released the 2.0.3 firmware update, they upped the bitrate from 30 Mbps to 44 Mbps – this new version of Magic Lantern moves the Canon EOS 5D Mark II (reviews) all the way up to a sustainable 66 Mbps

Magic Lantern changes for bitrate

The Canon function mvrSetDefQScale(int16_t *) (2.0.8 0xff990188) sets the quality parameter to the camera's h.264 encoder. If the CF card is not able to keep up, the camera will display a buffer-level bar on the right side of the LCD and stop recording when it hits full. The parameter does not have any effect unless fixed bit rate encoding is selected via mvrFixQScale(int16_t *) (2.0.8 0xff9905d4).

The default q-scale is -8 in VBR mode and has a nominal 42 Mbps with the 2.0.8 firmware. The 24p tests were done with the camera on a tripod writing to a Lexar 400x UDMA 16 GB card with all Magic Lantern tasks disabled (no zebras, cropmarks, etc). qscales less than -12 occasionally stopped recording.

Q-scale FPS Mbps Notes
+8 30p 7 Mbps Very low quality
-9 24p 32 Mbps
-10 24p 41 Mbps
-11 24p 51 Mbps
-12 24p 59 Mbps
-13 24p 62 Mbps
-14 24p 66 Mbps Best, sustainable in 24p mode?
-15 24p 68 Mbps 2 buffer bars
-16 24p 76 Mbps Only a few seconds


  • 24p seems to have less issues than 30p
  • Locked-off shots seem less likely to trigger buffer overflows; amount of motion?
  • Auto-exposure changes seems to lead to immediate overflows: shoot manual exposure mode
  • -14 seems to be the best that can be sustained with the card with all other ML tasks running.

Test firmware


What is bitrate anyway? Why do you care?

Many of you (including myself as well) are probably wondering why the bitrate matters. My first understanding was that it had to do with the speed at which data was written to the CF card (and to some degree it does) – meaning slower cards would have a problem with writing longer video files as the data coming off the camera was coming too fast.

But bitrate is more than just speed of writing to the card. Higher bitrates also mean higher quality video results and you'll get slightly larger files.

In the forum thread Scott Bell added: “My understanding is that theoretically you would get less artifacts because you are applying less compression to the signal. Likewise having more data for each frame would give you greater latitude with color and contrast. However I don't think a greater bit rate would alleviate problems like moire or rolling shutter.”

So, we also asked Trammel what he thought about the bitrate issue and he graciously sent us this tidbit:

“increasing the 5D's bitrate isn't as critical as it was on the GH1: going from 17 Mbps to 70 Mbps was a huge change, especially considering how uncompressed MJPEG is. The default 45 Mbps h.264 on the 5D Mark II is pretty good and most folks aren't reporting any significant improvement at the higher speeds and I haven't been able to quantify it.

I suspect that Canon selected a bit rate that was a good balance between the sustained data rate to the CF cards and where increasing the rate didn't make a significant difference to most viewers.

One neat thing is that the data rate can be turned way down, too, and still produce reasonable looking video for archival purposes. If you want to record at 10 Mbps, the 4 GB limit is now closer to an hour instead of ten minutes.”

We've also had a glance at Philip Bloom's post on the subject… good comment here:

This simply gives us better compression rates well less compression really. Obviously fast cards are needed and the video buffer clearly cannot cope with the high ones but it’s going to be fun to see how far the camera can be pushed…I know from tests that have been done the high bit rates don’t like a lot of movement in the frame either so a fair bit of work still to be done but it’s a great start.

Personally though the bit rate has never been the issue with the Canons, it’s the line skipping which causes the moire and aliasing. Increasing the bit rate is not going to fix this. This is a far more fundamental issue with the camera and I cannot see a firmware update fixing this. A new way of sampling the sensor is needed…for the GH1 it was different the 17mbp/s was simply too low. AVCHD 24mb/s is superb and of course the higher ones with the hack are even better. We just must not get too caught up in numbers. It’s not the bit rate that makes the camera and I guarantee you just by going over 50mb/s will not make it acceptable for full BBC HD acquisition!

Video Sample

Ok, now that you understand more about the bitrates, we've been chatting with Bill Abbe from who's been doing some testing of the new Magic Lantern version for the Canon EOS 5D Mark II. Here's what he's got to say:

It’s looking like 66 is the most stable and best image out of the group. I’m thinking of doing a low light test next. I think this is were the bitrate may shine. The one thing I did notice is the black levels look much cleaner with less noise. I’m going to do the candle comparison too and will also have a link to a high res download without compression. I’m finding the –14 at 66mbps is looking the best of the group. I was also only able to get the 76mbps on a tripod locked down. I noticed if the camera moved it would stop recording in about 2 to 3 seconds. I was also using a 32gb UDMA 400X Transcend Card.

Here's his latest testing video that might help you see some differences:

Canon 5d Mark II Comparison Test at Base Bit Rate and 76 MBps with Magic Lantern High Bit Rate Firmware – Test 2 from RockStar Media on Vimeo.

Shot on a Canon 5d Mark II with a 24-70 mm Canon L-Series Lens.

Comparing standard 5D bit rate settings and the new Magic Lantern Bit Rate Firmware at 66MBps and 76MBps.

No color correction done, straight out of the camera.

Canon 5D Standard Bit Rate

Using a Transcend 400X UDMA 32GB card.

Brought to you by FurryHead Windscreens for your Zoom H1, H4n and many other recorders…

And just to be complete, here's the one he did before that.

Canon 5d Mark II 76 MBps Test with Magic Lantern High Bit Rate Firmware from RockStar Media on Vimeo.

Shot on a Canon 5d Mark II with a 24-70 mm Canon L-Series Lens.

Comparing the 3 top bit rate settings on the new Magic Lantern Bit Rate Firmware.


Brought to you by FurryHead Windscreens for your Zoom H1, H4n and many other recorders…

Can you see any difference? Come over to this planet5D forum thread to discuss!

(Photo credit: snap from the video)

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