Fix FFmpegFrameGrabber to properly seek/skip the data inside custom InputStream

[teerapap]

The code previously did not respect InputStream.skip() return value. It leads to wrong seek result because the data might not be skipped to the desired offset.

It also assumed that the maximum input stream size is 1MB which might not be the case for bigger file. The problem arises when that the data after 1MB offset is read and the mark position is reset. It leads to InputStream.reset() not reset to the start of the stream as expected.

This merge requests

• Respect the InputStream.skip() return value
• Assume the input stream maximum size is at integer maximum.

[saudet]

Thanks! But we shouldn't force users to allocate 2 GB of memory to hold the whole stream. Let's make this configurable, via an optional constructor parameter would be best I believe.

[teerapap]

@saudet Thanks for the fast response. It is my bug that I pre-allocate big size of the buffer of BufferedInputStream. I fix it in the latest commit.

Calling mark() with big size does not mean the stream have to allocate the buffer with the same size. At least BufferedInputStream does not do that. It grows its internal buffer as needed.

I'll add another constructor to set this size then.

[teerapap]

@saudet If I add another constructor with optional maximumSize of the InputStream.
What should be the default value?

• 1024*1024 to be backward compatible.
  or
• Integer.MAX_VALUE-8 to cover bigger files by default and let the user set it to lower size if desired.

[saudet]

First, we need to pass it as argument to BufferedInputStream, or it won't work, so let's add that back. And we can't have something that allocates 2 GB by default, so let's leave it 1 MB by default yes.

[saudet]

Actually, it looks like you're right. Reading an MP4 file works even without passing the size of the buffer as argument to the BufferedInputStream, interesting. How does that work?

[saudet]

It does increase its internal buffer as needed. So, looks good to me as it is now. Thanks for the contribution!

[teerapap]

Thanks.