On Thu, Jan 22, 2009 at 11:40 AM, Sven Alisch <[email protected]> wrote:
> Hello Victor,
>
> Many thanks for your answer. That helps very much! I did not know that library
> but this will help!
> I suspected it, but I hoped that AVPacket gets a complete NAL-Packet. Does the
> ffmpeg-library will support this feature in the future? It will be nice,
> because ffmpeg has an h.264-decoder and with the x264-library an encoder.
>
> Or is it possible to give AVPacket a complete NAL-packet (readed and extracted
> with an other library) to write an muxer with the ffmpeg-lib?
>
> regards,
> Sven
>
> Am Donnerstag 22 Januar 2009 04:30 schrieb Victor lyamtsev:
>> AVPacket doesn't correspond to NAL unit at all ( if I understand
>> your dilemma).
>> If you need to quickly write NAL parser, look at the H264Bitstream
>> library at Sourceforge; You can find h264 stream parsing app with
>> example of how to use library there. Hope that helps...
>>
>> On Tue, Jan 20, 2009 at 8:31 AM, Sven Alisch <[email protected]> wrote:
>> > Hello,
>> >
>> > I'm sorry to be nerve-racking again with my bad english and my problem,
>> > but I want to start a new thread, because I know where my problem is, but
>> > I do not find a solution.
>> >
>> > First of all, i want to say, I want to update my cutting application with
>> > h.264-cut support. I must say, the ffmpeg-lib ist a really cool and good
>> > to use library and please don't get me wrong, I don't want to stress any
>> > libav-developer for implementing a special feature!
>> >
>> > My problem:
>> >
>> > The mpeg2-based features, I said it, are working fine. And now I was
>> > believing, that everything works automaticly with h.264 encrypted
>> > transportstreams. But no. They don't.
>> >
>> > The first thing, that irritates me is my following code:
>> >
>> > if (packet.flags & PKT_FLAG_KEY)
>> > {
>> > ...
>> > }
>> >
>> > After I read a single frame from a stream, I look, if it is a keyframe.
>> > This is working for mpeg2-files. But in an h.264 stream, is every single
>> > readed frame a key frame. And this is problematic. So my question is
>> > here, does this not work generally for h.264-streams?
>> >
>> > I thought ok and added for h.264-streams following if-clause.
>> >
>> > if (packet.data[i] == 0 && packet.data[i+1] == 0 && packet.data[i+2] == 0
>> > && packet.data[i+3] == 1 && packet.data[i+4] == 0x67)
>> > {
>> > cout << "IDR - Frame: " << frames() << " bei " << i << endl;
>> > avckey = true;
>> > allowParsing = true;
>> > ...
>> > }
>> >
>> > Now I see, it work better, but the decoder produces, if I want to extract
>> > a sequence, no pictures. The Decoder gave me no error messages, but every
>> > decoded picture has the same size. Really strange.
>> >
>> > So the next question is, does av_read_frame really read such a complete
>> > NAL-Packet or not?
>> >
>> > The last question is only for my own understanding. If I want to cut
>> > h.264-streams, then it is only possible to do that at IDR-Frames? Yes or
>> > no?
>> >
>> > Many thanks for any help!
>> >
>> > regards,
>> > Sven
>> > _______________________________________________
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>> > [email protected]
>> > https://lists.mplayerhq.hu/mailman/listinfo/libav-user
>>
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Hi Sven,
AVPacket cannot possibly be a separate NAL unit as it purpose to carry
data regardless of coding standard, so your suggestion doesn't make
much sense... H264 encoder is a separate entity from ffmpeg. You
should read AVPackets from ffmpeg into the circular buffer and parse
them into NAL units. You can hack H264Parser to do it but it faster to
use existing solution if you are in rush, if I've done it once and it
worked.
Here's the link to the lib:
http://sourceforge.net/projects/h264bitstream/
Look at the h264_analyze.c for the example.
Good luck,
-V
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