Apple ProRes codec reverse engineered

http://git.videolan.org/?p=ffmpeg.git;a=commitdiff;h=5554de13b29b9bb812ee5cfd606349873ddf0945

by kierank • 15 years ago

95 25 15 years ago

git.videolan.org

deweller• 15 years ago

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.

bradly• 15 years ago

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.

kierank2• 15 years ago

ffmpeg has been able to decode neither formats until now.

aschwo• 15 years ago

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?

johnbatch• 15 years ago

Haven't they had this for a while (Post Date: August 28, 2008). http://support.apple.com/downloads/Apple_ProRes_QuickTime_De...

However, it's nice that they have it built into ffmpeg now.

modfodder• 15 years ago

It's read only for Windows, so Win apps can't write out a prores file. (In reference to Apple's decoder)

protomyth• 15 years ago

The ARRI Alexa records in Apple ProRes 4444 or Apple ProRes 422. I am not sure if they got a license, but they have been doing it a while.

throwaway322• 15 years ago

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

dexen• 15 years ago

Your snarky remark can be read both ways:

  - if ffmpeg [developers] were overly scared about even remote risks of being sued, they'd stop.
  - if ffmpeg [developers] wanted to abide by the law, they'd have to stop.

and the second interpretation is quite unfair IMHO.

Keyframe• 15 years ago

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.

itsmemario• 15 years ago

but the patent licences fees still apply.

jpdoctor• 15 years ago

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?)

av500• 15 years ago

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

gst• 15 years ago

In countries where the patent applies.

flyosity• 15 years ago

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?

chime• 15 years ago

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.

beej71• 15 years ago

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 << exp_order) + (switch_bits + 1) << rice_order);

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.

daeken• 15 years ago

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.

baddox• 15 years ago

Would it be possible to write the same code to make it more readable without incurring a performance penalty? If not, then I guess it's okay, since these people have decided that performance is more important than readability (although there should be comments).

mdaniel• 15 years ago

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.

drv• 15 years ago

The King lives, and he's keeping busy by reverse engineering codecs...

  author	Elvis Presley <elvis@e.p>

bgentry• 15 years ago

I thought that was funny. Maybethe author is afraid of being sued over this? Otherwise why wouldn't you want to be recognized for this?

jasonwatkinspdx• 15 years ago

Reverse engineering can be done legally (in most jurisdictions) but that doesn't you want to invite an expensive lawsuit to prove you did it cleanly.

Apple ProRes codec reverse engineered

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