C100: C100 Mrk II, shooting AVCHD 28 mbps, 59.97p all the time?

[littlefish]

So we've decided to shoot AVCHD mainly due to the much higher quality audio. Shot some test footage AVCHD, 24 mbps, PF29.97 in Wide DR. Looks good. Then I shot just one scene AVCHD, 28 mbps 59.97p Wide DR and it looked sharper and cleaner than the slower frame rate on our HD studio monitor. Is it a crazy or even a bad idea to shoot at this frame rate, 59.97p? We do very little slow-mo. Pros/cons other than a tiny bit more real estate used on the cards?

 

[drummondb]

The only reason 60p has a higher bit rate is to maintain the same quality of 24p and 30p at the higher frame rate. The choice between 60p, 30p, and 24p should really be an artistic one. How does watching footage shot at those different frame rates make you feel? How do you expect it will make your audience feel?

Broadly speaking, 24p will have give your footage the motion characteristics of cinema, while 60p will give it the motion characteristics of live HDTV.

 

[pmcdonald]

Wouldn't another impact be on the effective bit rate? 60 frames spread over 28 Mbps gives an effective 0.46 Mbps per frame versus 0.8 Mbps per frame for 30fps@24Mbps. Am I understanding that right? Plus you have the exposure impact of having to double your shutter of course.

 

[littlefish]

Thanks for the info. I uncovered a few hours ago that Premiere CC was interpreting the Canon PF29.97 as interlaced, upper field first. So the footage look crappy compared to 60p in AVCHD and 60p in MPG4. Once I told Premiere (via modify) that the PF29.97 was progressive the footage looks great.

 

[Bruce Watson]

Wouldn't another impact be on the effective bit rate? 60 frames spread over 28 Mbps gives an effective 0.46 Mbps per frame versus 0.8 Mbps per frame for 30fps@24Mbps. Am I understanding that right?

Really, you're not. AVCHD is a long GOP CODEC. What's getting compressed is the differences between frames. So trying to average bits per frame is pretty meaningless.

The effect of frame rate on a CODEC like AVCHD isn't linear either. As frame rate goes up, the differences between the frames goes down. Which is why you can get by with a small bump in bit rate when you double the frame rate. The reason you need the bump is primarily due to the increased number of i-frames due to the higher frame rate.

 

[Scott F]

So we've decided to shoot AVCHD mainly due to the much higher quality audio.

I uncovered a few hours ago that Premiere CC.....

Hold on. From another recent thread (drummondb) :

The higher bitrate is only for the 60p frame rate. I don't notice any quality difference at all. In Premiere, the audio is instantly converted to floating 32 bit for editing, so I don't think the difference in audio will have any effect.

Frame rate aside, has anyone determined that the difference in audio quality is negligible when using Premiere? (mp4 vs AVCHD) Just wondering.

 

[littlefish]

First, I'm not an audio guy. Just hung out with a number of them over they years. My purest, by the book, audio buddies would say yes, there is definitely a difference. My non-purest audio buddies, would say, do some real world tests and make your decision from there.

I pulled this off an audio website: "PCM: Pulse Code Modulation. Also known a Linear PCM (one of the AVCHD options). PCM audio is an uncompressed, lossless storage system.

AAC: Advanced Audio Coding. AAC (the stock audio for MP4 in this camera) is a lossy audio compression format used in the Apple iPod, iPhone and iTunes music store."

However, my guess is that most people would not hear the difference in your final edited program unless you were recording a classical orchestra and the people watching the video were listening on a really high end audio system. Personally, I've always preferred to shoot with uncompressed audio when possible.