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AVCHD 1920×1080 Quality
Hi all,
just guessing what do you think about this: my camera is able to record at 1920×1080 50fps with a bitrate up to 28Mbps, and on same 1920×1080 25fps with a bitrate up to 24Mbps.
Don’t you think that the only 4Mbps of difference on 50fps vs 25fps don’t corresponding to 28Mbps-24Mbps?
I mean, the double of fps should have a bigger bitrate… I’m not saying the double bitrate, but,.. only 4?My eyes are not good for testing,… but, do you think that the quality at 1920×1080 at 25fps could be better than 1920×1080 at 50fps?
I know that at 50fps it should be better, but we’re having near the same bitrate with 25fps than with 50fps, and same amount of information on less fps it could be understand as better quality.What do you think?
Kindest regards.
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12 Replies
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My understanding is frames per second and bitrate are not two separate things that are not linked to each other in the way that you think…each is totally independent. For a more filmic look I would go with the 25fps.
Steve Crow
Crow Digital Media
http://www.CrowDigitalMedia.com -
I agree with Steve, go with 25p.
“There’s no point in filming if you don’t have fun”
Charles Meadows
Creative Director
Incubate Productions South Africa
http://www.incubatevideo.co.za -
Thanks for your answer Steve.
I understand about the filmic look,… but as I’m just want to know about recording quality, I’d like to focus on that question.
As far as I know (not much, sorry), the more bitrate, results in more quality (and bigger file). So, on same clip recorded at 1920×1080 and 25fps, a file with a bitrate of 24Mbps would be better quality than other at 17Mbps (we’re talking on same camera and lens), are you agree?
And, one minute clip file at 25fps it would be smaller size than the same minute recorded on same camera and settings, but at 50fps, are you agree?
Then, the only 4Mbps of difference between both (25fps vs 50fps) I find it weird. Why is this? is a codec’s limitation? Am I right if I think about a better quality on the clip recorded at 25fps (24Mbps) against the one recorded at 50fps (28Mbps)?Hope I can explain myself, but sorry, but my english is not good 🙁
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Thank you Steve,
but apart of the “looking”… what do you think about my question?Thank you.
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The reason that the file size at the higher bit rate isn’t much higher is because of the magic or efficiency of the compression code : better quality at just slightly higher file sizes
That’s what compression does – makes file sizes smaller while preserving apparent quality so you don’t see much loss from the missing data
Steve Crow
Crow Digital Media
http://www.CrowDigitalMedia.com -
I meant of course ARE two separate things
Steve Crow
Crow Digital Media
http://www.CrowDigitalMedia.com -
Thank you for your answer, Steve:
then, if is about a compression question, can we set that in this case, the 28Mbps file have a bigger compression? In that case, the more compression, less quality?
I mean, maybe the 25 frames per second are less compressed than the 50?Thank you!
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Hi,
Well, the frames per second is a totally different discussion that has nothing to do with what compression is being used. What we are talking about is really how much raw data is being captured by the camera’s sensor (bit rate) and how that data is being compressed (made smaller) by the AVCHD compression algorithm. So at both frame rates the compression is the same since it is still AVCHD compression.
Different codecs have different levels of compression – you don’t have much choice in this since the camera manufacturer chooses what codec to use. Now there’s the whole issue of transcoding the footage the camera gives you into a different compression format for editing (say into ProRes for example) but discussion of compression formats and what is really happening inside the video file becomes very technical after that point and I don’t know really anything really that.
Steve Crow
Crow Digital Media
http://www.CrowDigitalMedia.com -
Thanks Steve,
language is a wall sometimes. I’m really sorry about my bad English language… but, or I don’t understand you, or you don’t understand me. Please, apologize me, if when expressing myself I could look rude or so: it’s not my intention.
I find that the fps are on the discussion, because of the point I want to go to. Letting apart the benefits of recording at high frames per second (panoramics, slow motions,…) if only recording static clips at same resolution, same camera, same lens… just switching between 25fps and 50fps, and of course, thinking that we are recording at CBR (those 24fps and 28fps are VBR):
1 minute clip is a 180Mb file (at 24Mbps).
1 minute clip is a 210Mb file (at 28Mbps).This means that in the first clip, those 1500 raw frames are compressed in 180Mb, and in the second clip, those 3000 raw frames are compressed in only 210Mb.
So, does my approach make more sense now? Am I still wrong about my thinking?
Is there anybody who found a difference in terms of quality, between those two kind of settings?Thanks again.
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All video compression is “temporal” (time based) compression, so the quality of the final image will depend on how much visual information is changing during the length of your video recording.
Most of the time 60/50 fps frame rates do not need as much room to store the visual information because subjects we are filming do not move very much over the span of 1/60th or 1/50th of a second, so less data is required to store the information.
If you are filming very high speed events, then you would see a quality difference between the 60/50 fps video and the 24/25 fps video.
Bottom Line: for most normal speed video subjects the lower data-rate is fine for 50/60 fps recording.
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