Re: previous post [feature request]

[Thomas Johnson]

This is just a reply to my previous post, but because I promised I'll file a new request if you don't see a comment I posted on my previous request and therefore I'm filing new post here.

My previous post: ​https://trac.ffmpeg.org/ticket/6645

In my previous post I requested a feature: enable saving files to different extensions. Some people from your team responded saying that "Ffmpeg doesn't even determine format by extension, it determines format by file content". So, apparently you've missed my point. Ffmpeg may (and probably does) determine input format by file content. But, how in the world Ffmpeg can determine output file format by its content? What are you talking about?

Please read the previous post (if you didn't already), and more important: read my last comment on that post, because I don't want to repeat everything I've said in that comment. I will just remind you that in that comment I've said that I had postead a question about this on stack overflow, and ffmpeg experts responded that what I'm trying to do is not easy at all and that I probably need to file a feature request here.

And when I filed my first feature request, you said that it is invalid because ffmpeg determines format by file content and not by extension. I really have no idea what you were talking about. Ffmpeg cannot detect output file format by its content. Which content? Output file is not saved yet, about which content are you talking about.

You probably didn't even read my previous feature request carefuly. My feature request makes sense and if you didn't udnerstand what I had was talking about, then I can explain it more clearly if you want.

Simply, what members of your team said (in comments on my previous request, before it got invalidated) is outright false. How can ffmpeg detect output format by its content? Output file is not saved yet, it has no content. So, clearly ffmpeg detects output format by its extension.

Here is an example:

If I want to encode a png file into mp4 file, then I can do the following:

ffmpeg -hide_banner -i 1.png 1.mp4

But, what if I want my output file to be encoded as mp4 file, but to have file name "2.png"? For this particular case, it is possible by providing "-f mp4" commabnd line argument.

However, I asked on stack overflow: given extensions (lets say "mkv") and given output file name (for example "2.mp4"), which command line arguments one need to pass in order to encode file as mkv file, but file needs to be named "2.mp4"? It turned out (and ffmpeg experts explained it) that it is not easy. It is not easy at all, because each different extension require different arguments to be passed. As I explained in previous post, for example video files require "-f ext" where ext is target extension, and image files require "-f image2 -c:v ext". But, definitelly, it is not for all extensions and all video and image files.

I'm looking for a way to create a program which will for given file name and target extension (different from real extension) output command line arguemnts for ffmpeg required to encode file to that extension (like we passed original extension in file name). In my previous post in comment, members of your developer team explained that what I'm looking for is easy and that there is no need for feature request and that ffmpeg already detects format by file content and that extension is only fallback.

But, I've just explained here that no matter what you say, ffmpeg will never be able to detect output format by file content, because output file is not saved yet. There are two possibilities: 1) you've completelly misunderstood my previous post or 2) you didn't even read my previous post entirely.

Probably you underestimated (or didn't understand) what I was talking about. To explain it again, I'm not ffmpeg expert, but people on stack overflow know what they are talkign about. If it is still unclear what I'm requestion, then ask me what is unclear to you and I'll explain it again, as brief as I can.

IMPORTANT: Please don't post any comment here before you 1) Read my previous post, 2) Read my last comment on my previous post and 3) Read this whole post. I hope we will avoid further misunderstanding. Thanks.

[Carl Eugen Hoyos]

Please move this discussion to the user mailing list.