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Apple ProRes codec reverse engineered

git.videolan.org

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Re: Apple ProRes codec reverse engineered

#11

Post by chime »

flyosity wrote: post #9

This code makes me feel like I'm not even a real software engineer, I'm just a guy playing with kiddie languages working on kiddie problems. Anyone else think that after reading it?

Languages are just tools. What one person can write in Erlang or raw C, someone else can write that in JS or QBasic. What matters is what your code does. Having working on projects ranging from large ERP systems to audio DSP to video startup to joke sites like cakesy.com and iwannamarry.com, I can say that what matters most is how much you enjoy working on the project. That's it. If the twitter-feed-importing-app makes you happy and your users happy, don't feel bad that you're not contributing to OpenSSH.

Re: Apple ProRes codec reverse engineered

#12

Post by beej71 »

flyosity wrote: post #9

This code makes me feel like I'm not even a real software engineer, I'm just a guy playing with kiddie languages working on kiddie problems. Anyone else think that after reading it?

Codecs are complicated and mathy and optimized for speed. So you might find a line of code that says something like:

    val = SHOW_UBITS(re, gb, bits) - (1
and you just don't have a clue what it really means (I don't--even though I can easily read the line of code) because the answer is buried in the details of the codec design.

But trust me--if you go through a complicated spec and implement it yourself, you'll end up with a lot of similar stuff as this guy did, with his mighty-fine-looking piece of work.

Re: Apple ProRes codec reverse engineered

#13

Post by mdaniel »

flyosity wrote: post #9

This code makes me feel like I'm not even a real software engineer, I'm just a guy playing with kiddie languages working on kiddie problems. Anyone else think that after reading it?

I get what you're saying, but want to remind you that this kind of math is a skill just like juggling or swallowing swords. Just because some folks train more in web applications, ORM, crazy legacy file formats, whatever, does not automatically make them less of a software engineer.

I also quite often draw the distinction between "programmers" and "software engineers", with "computer scientists" sometimes being their own category, and sometimes a subset of the first two.

Re: Apple ProRes codec reverse engineered

#14

Post by throwaway32 »

aschwo wrote: post #3

This is a great development for decoding ProRes with non-OSX OSes. What are the legal implications? Will ffmpeg need to pay to license the ProRes codec from Apple? Does Apple even offer a license for the codec?

if ffmpeg worried about patents and licensing, they would have stopped development a long time ago.

Re: Apple ProRes codec reverse engineered

#15

Post by daeken »

beej71 wrote: post #12
flyosity wrote: post #9

This code makes me feel like I'm not even a real software engineer, I'm just a guy playing with kiddie languages working on kiddie problems. Anyone else think that after reading it?

Codecs are complicated and mathy and optimized for speed. So you might find a line of code that says something like: val = SHOW_UBITS(re, gb, bits) - (1 and you just don't have a clue what it really means (I don't--even though I can easily read the line of code) because the answer is buried in the details of the codec design. But trust me--if you go through a complicated spec and implement it yourself, you'll end up…

This is especially true when you're reversing a codec. I helped out reversing ALAC (Apple's answer to FLAC), and I didn't know what 99.9% of the code did, I just knew how it needed to do it. Certain things fit common patterns with simple changes (e.g. modified Rice coding), but most of the time you're just matching code behavior directly.

I will say, building an encoder based solely on the reverse-engineered decoder (didn't want to reverse out the encoder as well -- total mess) is a really fun challenge. Good way to dive into codec work.

Re: Apple ProRes codec reverse engineered

#16

Post by Keyframe »

aschwo wrote: post #3

This is a great development for decoding ProRes with non-OSX OSes. What are the legal implications? Will ffmpeg need to pay to license the ProRes codec from Apple? Does Apple even offer a license for the codec?

Windows is read only (although clipster somehow manages to write out prores files). There are two licensed products (hardware) that write out prores that I am aware of - ARRI Alexa cameras and AJA ki pro.

Re: Apple ProRes codec reverse engineered

#19

Post by av500 »

jpdoctor wrote: post #18
itsmemario wrote: post #8

but the patent licences fees still apply.

It's been over a decade since they haven't paid mpeg fees, so apple shouldn't hold its breath. (Do folks realize that ffmpeg has never paid such fees intentionally and as a matter of philosophy?)

it's not FFmpeg that would need to pay the fees, it would be FFmpeg users. A lot of codec royalties are tied to devices sold or hours of content streamed

Re: Apple ProRes codec reverse engineered

#20

Post by kierank »

bradly wrote: post #6
deweller wrote: post #2

From http://en.wikipedia.org/wiki/ProRes_422 : ProRes 422 is a standard-definition and high-definition lossy video compression format developed by Apple Inc. for use in post production. It was introduced in 2007 with Final Cut Studio 2 [1] and is comparable to Avid's DNxHD codec which has the same purpose and uses similar bit rates.

I believe ffmpeg has been able to decode ProRes 422 for a while now. It is ProRes 4444 that there hasn't been any decoding available for. It looks like this adds support for it.

ffmpeg has been able to decode neither formats until now.
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