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The latest official manual for Canon 60D says that a 1920x1080 movie with any FPS recorded takes up 330 MB/min.

The latest official manual for Canon 7D says that a recording with the same movie settings on this camera will also take up 330 MB/min.

Does this definitely mean both the cameras produce exactly the same results, or may it still be possible that one of the cameras produces worse video recording?

I'm sure it could be possible if those cameras were totally different, using different codecs for encoding, etc, but as those cameras are very similar and definitely using the same compression, I assume the aforementioned could be true, which makes me to ask the ultimate question: is the double DIGIC4 processor in Canon 7D useless when using it for shooting a video, compared to a single DIGIC4 processor in Canon 60D?

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3 Answers 3

up vote 5 down vote accepted

As you said, they could be 100% identical.

In all likelyhood they are not but given the bit-rate is the same for the same resolution, frame-rate and codec, I think it is safe to say that any difference will probably be negligible.

You are probably right that the second processor is probably not fully needed for video in this case. It is probably there to improve full-resolution continuous shooting.

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As we all speculate here, it is very probable that the output video is quite the same, or as @Itai put it, the differences will probably be negligible. However, there can be a difference induced by the fact that the 7D has double the processing power than the 60D, even when the bitrate is the same.

Video compression is based on encoding of differences of macroblocks from reference macroblocks (in reference frames). The underlying assumption is that scenes change relatively slowly, so compressing the difference in pixel values (in consecutive frames as well as in the same frame) is more economical than compressing the pixel values themselves.

So, the image is divided to a mesh of small rectangular macroblocks. Each MB is being searched for a best match (minimum cumulative difference) to an array of reference MB's. Ideally, you'd search for a best match in a full reference frame. Due to limited processing power and bandwidth, the search is restricted to the immediate surroundings of the MB being processed.

Having more processing power lets you search for a best match in a greater area, possibly giving better quality of the compressed video.

[Note that this description is really in a nut-shell and the actual process utilizes many steps and techniques, but this is the heart of it]

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I think for practical purposes, the fact that they essentially use the same sensor and record at the same bit rate and resolution and that the only significant differences between the two models are not really related to video (auto-focus doesn't apply to manual-focus video), I would say it's going to be difficult to choose one over the other.

Obviously if you're a photographer first, videographer second, the 7D still packs some better features, but the 60D's Tilty Swivelly Screen Thing™ is a big feature for shooting video between the two models.

I would for all intents and purposes look beyond the video recording for your comparison of the two models as they'll essentially produce the same output.

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