Introducing FLVSlicer (slicing and merging capabilities)

Recently I wanted to do some simple video slicing in AS3 with FLV's. I did not found any library for that so here is FLVSlicer !

FLVSlicer allows you to extract a "slice" of an FLV at runtime, but also merge multiple slices if you need to. The library may be really useful if you want to get a specific part from an FLV with no server involved. Ley's say for instance that you are looking for a specific text content in a video and you would like to save it on your hard disk or post it on youtube.

The API is really simple :

//create the FLVSlice object
var slicer:FLVSlicer = new FLVSlicer(new flvBytes());

// listen for the SlicedEvent.COMPLETE event
slicer.addEventListener( SlicedEvent.COMPLETE, onSliced );

// extract the slice with the specific timing (in ms) and save it
var firstSlice:FLVSlice = slicer.slice(1000, 3000);

// extract another slice with the specific timing (in ms) and save it
var secondSlice:FLVSlice = slicer.slice(7200, 8900);

// create a FLVSlice vector
var slices:Vector.<FLVSlice> = new Vector.<FLVSlice>();

// store the slices
slices.push ( firstSlice );
slices.push ( secondSlice );

// merge them as a single FLV stream
var merged:FLVSlice = slicer.merge( slices );

The tricky thing was to update each frame timestamp (NetStream.time) without creating any backward timestamp. Then, the onMetaData duration tag is modified so that the sliced FLV works smoothly in the Flash Player. When calling the slice() method from the FLVSlicer API, it will automatically find the nearest keyframe and cut from there. For the ending point, it will slice it with no nearest keyframe behavior.

To illustrate its usage, here is a little demo of the slice() method :

A Flash animation should have appeared here, but it seems that your browser has an older version of the Flash Player or it is not installed at all. Please, install the last release of the Flash Player now, then reload this page.

Merging multiple slices will be available in the next release :)
Merging multiple slices is available since version 0.3.

The current limitation right now with the Flash Player is that you cannot inject the new generated FLV in the NetStream class you have to send it to a server and load it again, damn, do you remember a similar story ? This is now possible with Flash Player 10.1 (NetStream.appendBytes).

Other limitation, when loading a video through the NetStream class, you cannot access the video bytes, so you have to load the video twice : Embed tag to access the video stream and use the traditional method to play the video.

So please, vote for adding byte access to the NetStream class.

This request has been opened by Benjamin Dobler who created RichFLV a very cool AIR app which does some FLV editing.

Sources from the demo above are available here.
Thanks for the cool components Keith ;)

Update : Version 0.3 adds a merge(slices:Vector.<FLVSlice) method to merge multiple FLVSlice objects into a single FLV stream.

Comments (43)

  1. Mem's wrote:

    Hi, for reading FLV on the fly you can inject it in SWF generated on client side, like for fonts :

    But this not work for other video containers like MOV or MP4

    Monday, August 10, 2009 at 8:52 pm #
  2. Thibault Imbert wrote:

    Hi Mem’s,

    Very cool workaround, tks for the link ;)


    Monday, August 10, 2009 at 8:55 pm #
  3. Jloa wrote:

    Wohoo, nice post as always.
    Btw, Thibault u’ve received my email? ^_^

    Tuesday, August 11, 2009 at 1:45 am #
  4. Antonin wrote:

    Excellent !
    Bravo Thibault

    Tuesday, August 11, 2009 at 10:12 am #
  5. Thibault Imbert wrote:

    Hi JLoa,

    Yes ! Concerning the “Contributors” section right ? I am happy we could help, feel honored to be in the credits ;)



    Tuesday, August 11, 2009 at 10:36 am #
  6. Benz wrote:

    Hey Thibault,

    nice work! I`m happy to see this as I was not able to release my code due to an arrangement with my current client and a lot of people requested the code.
    One thing on you example the name of the video suggests that it`s a H264 but I think it`s a VP6. I never managed to actually implement H264 support. Would be awesome if you do ;-)
    Keep up the great work

    Tuesday, August 11, 2009 at 12:43 pm #
  7. Thibault Imbert wrote:

    Hi Benjamin,

    Thanks for your comment. I am very happy that you like it :)

    You are right, it’s a VP6 file, the name was not updated after encoding it. Btw, I will take a look at H.264 support, but yes seems definitely much harder :)



    Tuesday, August 11, 2009 at 1:26 pm #
  8. fab wrote:

    C’est vraiment énorme !
    Excellent !
    A mettre das la TODO de “A Deep Dive into Ten Innovative Projects for Flash” ;)

    Friday, August 14, 2009 at 10:32 am #
  9. wvxvw wrote:

    Hi Thibault.
    Exciting work!
    And, I was actually thinking about making on-the-fly video encoder for SWF. If that was any way possible that would be really awesome… For now I’ve tried generating sound assets from byte stream only… I realize video would take much more work, but it should be doable, as there are specs for embedded video.
    This is what I have for now.
    So, if you would ever consider starting this kind of project, I would be more then willing to help, if I can :)
    Anyway, happy coding!


    Saturday, August 15, 2009 at 1:10 am #
  10. Muhammad1 wrote:

    I downloaded you Demo zip, ran it, and it says your slicer class doesn’t have a “Start” and “End” function:

    1061: Call to a possibly undefined method start through a reference with static type


    1061: Call to a possibly undefined method end through a reference with static type

    ..which is true because these functions really don’t exist inside the FLVSlicer.

    And its talking about line # 160 of your

    Am I doing something wrong?

    Tuesday, August 18, 2009 at 12:20 am #
  11. Thibault Imbert wrote:

    Hi Muhammad1,

    Download the .zip file again. I have just updated the files. It should work smoothly :)

    let me know,



    Tuesday, August 18, 2009 at 1:59 am #
  12. Muhammad wrote:

    Dear Thibault,

    I’m without a doubt one of your biggest fans. I tried your updated archive, and now when I run it, it says this:

    Error: Error #2030: End of file was encountered.
    at flash.utils::ByteArray/readUTFBytes()
    at FLVSliceTest()

    Tuesday, August 18, 2009 at 9:37 am #
  13. Thibault Imbert wrote:

    Hi Muhammad,

    It seems like the video is not correctly embedded. Are you compiling the project through Flash CS4 or Flash Builder ?

    let me know :)


    Tuesday, August 18, 2009 at 9:50 am #
  14. Muhammad wrote:

    I’m using Flash CS4, not flash builder. It does compile nicely, without errors. It just gives an error when I have it compiled. Doesn’t show any button, just blank screen. Here is all I see when I compile it:

    If this was a problem with CS4, it would say something like a syntax error or similar, right?

    Tuesday, August 18, 2009 at 8:09 pm #
  15. Thibault Imbert wrote:

    Hey Muhammad,

    It’s really strange, I don’t see any problems. It seems like the embedded movie is empty at runtime, I am pretty sure the embed tag does not work properly.

    Can you try replacing the flvslice.fla you have with this one ?

    When compiling, it will ask for the Flex SDK path because of the Embed tag. Just click the update the path button and recompile the movie again.

    let me know if this works :)


    Wednesday, August 19, 2009 at 1:13 am #
  16. Thibault Imbert wrote:

    Hi again Muhammad,

    Try downloading the sources again. I have just repacked everything with no dependencies problem. I tried on another computer and it works.

    let me know,


    Wednesday, August 19, 2009 at 11:05 am #
  17. Lamoureux D. wrote:

    Salut Thibault.
    Beau boulot! J’ai cependant le même problème que muhammed . Je remplace le .fla , question sur le Flex path(“update”).
    Je recompile , et ça ne marche pas.

    Wednesday, August 19, 2009 at 7:37 pm #
  18. Lamoureux D. wrote:

    that works. Sorry =) Good Job

    Wednesday, August 19, 2009 at 8:26 pm #
  19. Thibault Imbert wrote:

    Salut Lamoureux,

    Cool, tu me rassures ! Je comprenais plus là ! :)


    Wednesday, August 19, 2009 at 10:06 pm #
  20. Tony wrote:

    Salut Thibault,

    Très pertinent ! Peux-tu m’indiquer les documents (specs du format flv..?) que tu as consultés ? Merci d’avance.

    J’ai voté pour l’accès aux octets du flux NetStream. J’attends çà depuis un bon moment !!


    Monday, August 24, 2009 at 12:09 am #
  21. Thibault Imbert wrote:

    Salut Tony,

    Tout est là :)

    Merci pour le vote ! ;)


    Monday, August 24, 2009 at 9:28 am #
  22. Muhammad wrote:

    Hi Thibault,

    I’m sorry for the very late response. Basically I got myself busy with a project so almost forgot to write back on your blog.

    First of all, I am still unable to run it with all the new files as well. It gives exactly the same message, byte array is going past something which I don’t know what it means.

    However, what I have come to understand from this so far is that the only problem we’re having with implementing this is probably just that we have to embed the video and we can’t use external videos with this.

    I had a solution to that. My solution is that if we can make this code a Pure ActionScript code (which can be compiled from DOS or Linux’s Terminal using the Flex Builder) we can over come this issue.

    The idea that came to my mind right away was to make the actionscript a text file and do all the visual drawings as well via the AS to make a UI for normal users. Before the come to the flash page they will go to a normal HTML page which asks them to upload a FLV. That FLV is saved on the server, and PHP edits the ActionScript file (which is a text file at the moment) and tells PHP to tell the compiler to compile the file. Once compiled, the user is redirect to the page (we can ask them to wait a particular amount of time before they are redirected).

    Now, the newly generated SWF will have the video embedded with what they just uploaded. And we’ll have the issue pretty much solved.

    Do you think this could work? Because if you can find a mistake in this I will probably not worry about running this script on my computer as it won’t be of any use. I’d really appreciate if we could someday talk on Skype. I am a self-taught ActionScript programmer and have literally never talked with a programmer who does ActionScript. My Skype is “Khanqah.”

    Thank you very much.

    Friday, August 28, 2009 at 11:25 pm #
  23. wvxvw wrote:

    Hi Thibault.
    Just wanted to let you know that I actually made it, i.e. here’s how you can compile FLV into SWF and then play it in the Flash Player, please find the sources here:
    And AIR app for testing:

    I will be very pleased to hear feedback! :)
    The code is quite raw atm, but a couple of tests I made worked. I still need to discover few things about PlaceObject2 tag, yet, apart from that thing nothing seem to be complicated.

    Wednesday, September 2, 2009 at 6:21 pm #
  24. Thibault Imbert wrote:

    Hi Oleg,

    This is great ! Thanks for the great work. I am currently in holidays so I cannot try it :) As soon as I come back I will plug it with FLVSlicer it is going to be really nice !



    Wednesday, September 2, 2009 at 11:50 pm #
  25. Hey Thibault.

    While on holiday, will you be completing your book?

    Tuesday, September 15, 2009 at 9:12 pm #
  26. Thibault Imbert wrote:

    Hey William,

    Which book are you talking about ?



    Wednesday, September 16, 2009 at 9:14 am #
  27. Thibault Imbert wrote:

    Hey William,

    I think you were talkin about the “What can you do with bytes” book right ? I actually finished the first chapter and still have a lot of work. I had to pause the writing cause I had a big project at Adobe, but I will be back on it very soon :)


    Wednesday, September 16, 2009 at 7:16 pm #
  28. Julien wrote:

    Salut Thibault, super ta librairie. Je me demandais si tu avais un exemple d’utilisation avec OSMF et plus particulierement VideoElement,

    Monday, May 31, 2010 at 6:37 pm #
  29. ATIF wrote:

    Hi Thibault,
    I am trying to use appendBytes with virtual file.But no success.Video player only Shows First Frame and the nothing after that.Any suggestions. regards,

    Saturday, July 31, 2010 at 7:28 pm #
  30. matt wrote:

    Hi everyone. Fantastic work on FLVSlicer. It is exactly what we needed for our software, except for the fact that it doesn’t seem to work with audio-only streams where there may not be a keyframe(s) present. Is there any way to make this work with audio-only?


    Thursday, November 4, 2010 at 6:22 pm #
  31. Manuel Lama wrote:

    I know how to fix error 2030 when embedding another flv which is not the original one.

    I use a video converting program to convert from flv to flv. Yea. It may sound strange, but…it works. I dont know why, but it works.

    Anyway, how could I use two o more videos and get several parts from them and join them…

    Friday, November 19, 2010 at 9:27 pm #
  32. scott wrote:

    I’m interested in merging video slices together, but so far there seems to be small jumps when you do this. Here’s an example of the jumps Would this library allow merging of video together on the fly and prevent the ‘jumps’ between slices?

    Thursday, December 2, 2010 at 11:48 pm #
  33. patmat wrote:

    There’s a “sound” getter in FLVSlicer. Can that byteArray be played with a Sound object using the SampleDataEvent.SAMPLE_DATA event? I tried this code but I can just hear noize.

    byteArray = slicer.sound;
    byteArray.position = 0;
    sound = new Sound();
    sound.addEventListener(SampleDataEvent.SAMPLE_DATA, processSound);;

    private function processSound(event:SampleDataEvent):void {
    if (! byteArray.bytesAvailable > 0) {
    trace(“Play Data – NO DATA”);
    for (var i:int = 0; i < 4096; i++) {;;

    Friday, February 4, 2011 at 4:14 am #
  34. Matthieu wrote:

    Bonjour à tous,

    Pour les développeurs actionscript français, j’ai effectué une vidéo d’explication pour utiliser flv slicer :

    A bientôt,

    Thursday, July 7, 2011 at 9:33 pm #
  35. greg wrote:

    And I don’t understand why you say you can’t play the video on the fly. I just did that (i sliced a video, moved the slices in random order, and then merged them). I’m doing NetStreamAppendBytesAction.RESET_BEGIN before appending the ByteArray and I plays perfectly.

    Tuesday, July 19, 2011 at 10:29 pm #
  36. Thibault Imbert wrote:

    Hi greg,

    Happy you like it!

    Actually, when I wrote this, Flash Player did not have the NetStream.appendBytes capability. I edited the post ;)

    Thanks for catching this.


    Wednesday, July 20, 2011 at 5:29 am #
  37. Manuel Lama wrote:

    Hi there, everyone.

    I was able to mix two different videos changing a little the Thibault FLVslicer classes. Hope you enjoy it!

    For further reference, you can contact me at

    You need two videos with the same codec information or the conversion will fail. Convert two videos with the video converter you prefer.

    Friday, August 12, 2011 at 7:18 am #
  38. Parmy wrote:

    Hi Thibault

    Fantastic post – thank you for sharing.

    I’ve fallen over at the first hurdle, on the following line:

    // create the FLVSlice object
    slicer = new FLVSlicer(new flvBytes());

    The error messaging I’m getting is:

    TypeError: Error #1007: Instantiation attempted on a non-constructor.

    I guess it’s saying I can’t instantiate a Class.

    I’m using Flash Builder 4.

    Any suggestions?



    Friday, October 14, 2011 at 7:40 pm #
  39. Raja Jaganathan wrote:

    Great work.I want to play flv byte array instead of embedded flv byte array.For example you code like“somefile.flv”) here my case what i put here ?Because i not embeded anything with local. .Initially i have encrypted flv file that i need to convert to ByteArray (decrypted one and not stored in local system or anywhere) then i need to play.How to do this ?. please help me.

    Monday, November 21, 2011 at 10:04 am #
  40. Anand Meena wrote:

    Hi Thibault,

    I download your code and trying to run it on flash builder 4.6 .

    I am unable to run this code.

    Can you please give me a working code example with flash builder 4.6 .

    Appreciate your help.


    Friday, January 6, 2012 at 9:18 am #
  41. ruly wrote:

    same with Parmy, problem is I can’t instantiate a Class. new flvBytes()

    it says TypeError: Error #1007: Instantiation attempted on a non-constructor.

    any clue Thibault?

    Saturday, March 10, 2012 at 3:39 am #
  42. lebobas wrote:

    Has anyone been able to use this technique to append two video clips together? Or same clip but with two headers.

    Friday, February 22, 2013 at 11:40 am #
  43. Anthony Sherritt wrote:

    Great work! I’m confused on a few things though. I’m trying to create a web app that allows you to pull in videos from facebook, and slice them into “subClips” not using FMS. Does the video you slice always need to be embeded, or is it possible to load a progressive video and slice that?

    Thursday, October 3, 2013 at 3:09 am #

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