Finding closest IFrame position in bytes in an MP4 file from the time offset position

[Sanjay Madhavan]

I am trying to implement a HTTP Pseudo streaming solution for MP4 files.

One of the issues I am facing is that the client video player can optionally send a start parameter that refers to the offset in seconds within the mp4 file being streamed.

 e.g: /stream?file=sample.mp4&start=30.45

I am trying to figure out based on the start parameter the closest IFrame position (in bytes) to that offset and start streaming from that point.

Any suggestions?

/sanjay

[Sanjay Madhavan]

I meant key-frame not IFrame

[NITIN GOYAL]

offset in seconds?

Cant this be managed as cue points putting them into the header boxes?

Using the different box tables we already have the position of all the offset values so i think it can be managed easily.

[Sanjay Madhavan]

Nitin,

Thanks for the reply.

Yes. Offset in seconds.

What I want to do is given an offset in seconds find the closest key-frame in the file and return the offset in bytes of the key-frame so the server can stream the file from that byte offset

Not exactly sure whet you mean by cue points.

Would you have a sample of something I can look at to get started?

/sanjay

[NITIN GOYAL]

Yeahok.

That is pure pseudoStreaming.

If you streaming on HTTP you can us the HTTP byte ranges as well.

For the mp4 file also, you need to associate the Keyframes with the timings like if your data is 25fps, then at 30th sec u know which frame will come and thus you will be able to calculate the required offset as well and then decode that particular NAL and the subsequent ones.

but every file which don't have the equal number of frames or don't ave a predefined GOP size, it will be difficult to manage i guess as you don't know which frame to call.

There are few solution which implements pseudo Streaming.  You may take a look on the source code of this http streamer:

http://flash.flowplayer.org/plugins/streaming/pseudostreaming.html#prepare

it is not calling using the timestamp but using the frame number but the similar thing can be manged by ,mapping the offset of the key frame with the timestamps.

[Sanjay Madhavan]

I am implementing the server side so need to figure out where to start streaming for given a time offset.
byte ranges does not work for mp4 files hence need to figure out the timeoffset->byte position map

/sanjay

[Sebastian Annies]

This should do it:

http://code.google.com/p/mp4parser/source/browse/trunk/examples/src/main/java/com/googlecode/mp4parser/ServeMp4.java

2012/10/16 Sanjay Madhavan <sanjay....@gmail.com>