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Digital formats: separate frames or not?
Hello,
I’m not sure this is the right forum for my simple question, and excuse me if my question sounds a bit silly, but I hope anybody can give me a simple answer?
In my mind film was always equal to ‘frames’. I have an animation background, so that is quite clear to me.
My question:
Is it wrong to say that digital formats (Quiktime, Mpeg, …) also are built up as frames, one after the other -digitised, compressed, checked and corrected, whatever- but still ‘frames’ -in a digital form, as one’s and zero’s- , one after another? If a file like that is read or opened or ‘played’, can we say correctly that the frames are read, one after another to be displayed or processed, for checking purposes for instance?
Or do i have to see it differently, and can I not see it like that, and is the digital information stored in another way, not as separate images anymore?
There is no real practical reason why I ask this, it’s just I want to understand better the way digital film-files are built up…
Thanks in advance,
geert -
1 Reply
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Video file are broken down into in the following:
Container – .MOV, .AVI, .MXF, .MP4 – The container has rules about the format of the data that can be put into it. The container can hold a single video stream and 2 channel audio or multiples of both.
Video COmpressor DECcompressor – h.264, Prores, DNxHR, ect
Compression comes in different forms like Intra Frame and Group of Pictures. Bitrate specifies how much information is thrown away, or used to record frame info.
Intra frame is the most like film where the frames are compressed individually, Uncompressed, Prores, DNxHR, XAVC-I, Cineform, AVC-Intra work like this.
Group of pictures looks at series of frames and records the difference between frames, MPEG-2(DVD), XDCAM, AVC/h.264 works like this for example.
Audio is encoded along with the Video stream in a format that is specified by the container. Audio can be encoded compressed like MP3, AAC, AC-3(multi-channel mp3) or uncompressed (PCM). .AVI means AV interleave which describes how the Audio and Video are written inside the file.
For animation work, you would want to render your animations aligning to the video frame rate standards of your delivery format. Normally this would be 23.97, 29.97, 59.94(60P or 60i) and almost never even rates like 24, 30, or 60. You need to know the specs your delivery format before you render.
Resolution standards like 4k are not supported by all codecs. Animation renders should conform to resolution standards of the video delivery codec.
Animations are often delivered as image sequences in .EXR, .PNG, or .TIF. Formats like .EXR support layers+alpha like photoshop files. .PNG supports alpha-channel, so that animation layers can be later controlled in the compositing and editing stages. Most editing software will import image sequences and treat them like video files. This maintains the animation quality, and allows for individual frame change without rendering a whole new complete sequence file.
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