Question about seeking after the file has been downloaded

[RobbieFernandez]

Hi, I'm using this library to stream mp4 files remotely and it's been working really well so far. I just have 1 question about the way in which .seek is intended to be used. I'm using mp4box for generating samples and then using the webcodecs VideoDecoder API to decode and present the samples.

The main reason I'm using this library instead of an existing out-of-the-box player is because I need the ability to jump to specific frames with 100% accuracy. This is working quite well while the file is being fetched in the background, using .seek() to jump to the nearest RAP and then discarding frames until I reach the target. However once the file has been fully downloaded, calling .seek() will no longer trigger the .onSamples callback. Looking through the code for this library it looks to me like what happens is .seek updates the nextSample attribute but doesn't actually initiate any sample processing. The reason I'm getting the samples while the file is being fetched is because I'm calling .appendBuffer which does eventually trigger sample processing. So my workaround for this is to just call .seek and iff the file has already been fully fetched then also explicitly call processSamples(false)

I'm wondering if this is working as intended, or if I'm misunderstanding the way in which .seek should be called?

[SiddeshSharma]

How can i calculate bytes of data required for demuxing next n frames of mp4 file?

[selsamman]

@RobbieFernandez - I had wondered about that as well. In my case I was using segments rather than samples and onSegment was not firing after the file was downloading and seeking back in the file. What worked for me with segments was to make sure that mp4box was discarding it's buffers. Only then would seeking backwards cause onSegment events to fire. It might be the same for samples as well. So the process is:

• Create the file with a false parameter mp4File = MP4Box.createFile(false);
• Call seek and get the new file position of the last RAP filePosition = mp4File.seek(from, true).offset;
• Append buffers at the requested file position and onSegment fires and I imagine onSamples would as well