[FFmpeg-devel] Animated GIF support

[Don Moir]

----- Original Message ----- 
From: "Paul B Mahol" <onemda at gmail.com>
To: "FFmpeg development discussions and patches" <ffmpeg-devel at ffmpeg.org>
Sent: Wednesday, December 19, 2012 7:55 PM
Subject: Re: [FFmpeg-devel] Animated GIF support


> On 12/20/12, Don Moir <donmoir at comcast.net> wrote:
>>
>> ----- Original Message -----
>> From: "Paul B Mahol" <onemda at gmail.com>
>> To: "FFmpeg development discussions and patches" <ffmpeg-devel at ffmpeg.org>
>> Sent: Wednesday, December 19, 2012 7:41 PM
>> Subject: Re: [FFmpeg-devel] Animated GIF support
>>
>>
>>> On 12/19/12, Don Moir <donmoir at comcast.net> wrote:
>>>> ----- Original Message -----
>>>> From: "Vitaliy Sugrobov" <vsugrob at hotmail.com>
>>>> To: <ffmpeg-devel at ffmpeg.org>
>>>> Sent: Sunday, August 12, 2012 9:15 PM
>>>> Subject: [FFmpeg-devel] Animated GIF support
>>>>
>>>>> Hi. I would like to participate in development of animated gif decoding
>>>>> support.
>>>>> Actually i've already implemented this feature by adding gif demuxer
>>>>> and
>>>>> slightly changing
>>>>> existing gif decoder, but it is not complete yet. There is a problem
>>>>> with
>>>>> variable delay between
>>>>> frames in gif: i cannot make it work. I tried to set time base via
>>>>> avpriv_set_pts_info (1 for numerator, 25 for denominator) in my
>>>>> demuxer's
>>>>> gif_read_header(),
>>>>> at the same time in gif_read_packet() i set proper pts, dts and
>>>>> duration
>>>>> for each succesive packet.
>>>>> But it doesn't work: conversion from gif to any kind of video gives me
>>>>> output with
>>>>> 25 frames per second rate and constant delay between frames. Please
>>>>> point
>>>>> me in the right direction.
>>>>
>>>> I don't use ffmpeg for gif's but did a comparison of latest gif patches
>>>> and
>>>> found some problems with ffmpeg animtated gif support.
>>>>
>>>> Several had no transparency which should have been transparent and hears
>>>> a
>>>> couple samples of that:
>>>>
>>>> http://sms.pangolin.com/temp/chompy.gif  - shows gray background
>>>>
>>>> http://sms.pangolin.com/temp/cool.gif  - shows black background
>>>>
>>>> This one gets transparency right but seems to have the wrong delay. The
>>>> delay value I get is 15 which is 150ms. With ffmpeg its way
>>>> to fast.
>>>>
>>>> http://sms.pangolin.com/temp/crazy.gif  - 2 frames and animates too fast
>>>>
>>>> This one caused me to crash in avcodec_decode_video2:
>>>>
>>>> http://sms.pangolin.com/temp/heart.gif
>>>>
>>>> I have many more gifs that may cause problems and if you decide to fix
>>>> the
>>>> above I will test it some more. All of the above
>>>> displayed normally outside of ffmpeg.
>>>
>>> Please open bug report for such problems. At least I can not keep
>>> track of all mailing list threads.
>>
>> Since I do not use ffmpeg for most image types and probably never well,
>> consider this a public service that I at least spent some
>> time testing it more completely. I don't wish to spend any more time on it,
>> but if fixes are made I will test it. If someone wants
>> to file bug reports then have at it. I think to often patches are made
>> without complete testing.
>
> So you are saying that gif animation support should be removed?

To me I don't care if you have animated gif support in ffmpeg since I don't use ffmpeg for that, but I am sure it matters to some 
that expects it to behave correctly.

> People are not perfect so expecting perfect code is pointless.

I don't expect perfect code, but it took me less then 10 minutes to come up with mulitple problems. When I test something, I do a 
number of tests and comparisons and still don't always get it right but give it a good shot.

I think its up to Vitaliy to set it straight.