[Libav-user] newb mp4 question

[Atli Thorbjornsson]

Thanks Dan. Looks like this is a dead end then. The Android is unable
to stream aac unless contained in mp4/3gp.
Strange but unfortunately true. We will need to decode as well.

Thanks again for your help,
Atli.

On 5 October 2011 23:35, Dan Haddix <dan6992 at hotmail.com> wrote:
> You can't falsify the MOOV atom because it contains file offsets to the
> individual data blocks, and you wont know what those offsets are until the
> data is written. If you need to stream realtime then MP4 is not a good
> format.
>
> I didn't realize you were only streaming audio though. In that case you
> don't really need a container at all. You can stream raw AAC frames as long
> as they have an ADTS header attached. You only need a container if you need
> to interleave audio and video data, or if you need timestamps for seeking.
> If you're just streaming in real time then sending raw frames should work
> fine.
>
> Dan
>
>> Date: Wed, 5 Oct 2011 23:05:16 +0000
>> From: atlithorn at gmail.com
>> To: libav-user at ffmpeg.org
>> Subject: Re: [Libav-user] newb mp4 question
>>
>> Thanks Dan, when we stream live we often falsify the content-length to
>> something like 2gb, users are never going to hit that limit with
>> normal usage so it's "good enough". The underlying http client will
>> often cut off at that point which is fine, people will forgive
>> restarting a stream after 2gb of listening.
>>
>> Could I use QTFastStart and provide similarily false information to
>> the container so it could at least start streaming?
>>
>> While I have you on the line ;) what transport stream should I
>> otherwise be looking at. I don't have a lot of options to choose
>> from....
>>
>> Atli.
>>
>> On 5 October 2011 22:38, Dan Haddix <dan6992 at hotmail.com> wrote:
>> > MP4 files contain something called a MOOV atom, which contains vital
>> > information about the file that is needed for playback. The MOOV atom is
>> > not
>> > written until you call av_write_trailer. And even then it's written to
>> > the
>> > very end of the file which makes it so you can't stream the file. There
>> > is
>> > another chunk of code in FFmpeg called QTFastStart which moves the MOOV
>> > atom
>> > to the start of the file, which in turn makes it possible to stream the
>> > file, but you still need a finished file before you can call it. So it's
>> > really only meant for streaming complete files from a server to a
>> > player.
>> >
>> > If you need to remux and stream in realtime then you'd be better off
>> > using
>> > another format. Transport streams are the best for streaming. They have
>> > no
>> > header or footer and can be picked up at any point in the stream without
>> > issue. This is why broadcasters use TS for digital TV signals.
>> >
>> > Dan
>> >
>> >> Date: Wed, 5 Oct 2011 22:18:24 +0000
>> >> From: atlithorn at gmail.com
>> >> To: libav-user at ffmpeg.org
>> >> Subject: [Libav-user] newb mp4 question
>> >>
>> >> Hi, I'm trying to remux an flv muxed aac stream using the mp4 muxer.
>> >> (movenc.c). It works fine so long as I call av_write_trailer.
>> >>
>> >> Problem is I also need to remux live (long running) streams, how would
>> >> I go about that. Currently a skeleton of my code looks like this
>> >>
>> >> init_input
>> >> init_output
>> >>
>> >> do{
>> >> av_init_packet(&ipacket)
>> >> av_read_frame(iFormatCtx, &ipacket);
>> >> if(packet.stream_index == audioStrem){
>> >> av_init_packet(&opacket);
>> >>
>> >> copy stuff around, code borrowed from ffmpeg.c
>> >>
>> >> av_write_frame(oFormatCtx, &opacket);
>> >> av_free_packet(&opacket);
>> >> }
>> >> av_free_packet(&ipacket);
>> >>
>> >> }while(stuff is incoming);
>> >>
>> >> av_write_trailer(oFormatCtx);
>> >>
>> >>
>> >> I was hoping I could buffer av_write_frame calls and write out to a
>> >> client but the client can't understand the file without the trailer it
>> >> seems. I'm new to this stuff so I was hoping someone could point me in
>> >> the right direction.
>> >>
>> >> Before you ask, I am streaming to the Android MediaPlayer so my format
>> >> options are a little limited.
>> >>
>> >> Thanks,
>> >> Atli.
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>> >
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