Hello
The information you passed will help me later, thanks. In this moment,
my application communicates with an embedded product which sends only
one frame per NAL in this moment. Later, it will send inceed multiple
slices, and we said that we will see what we are going to do then. Is
there any possibility to find which slice is the start of a frame
sequence and which slice is the end of it? In you case for example, is
there a possibility to find the first 5 from I frame and the last 5
from I frame (or, the first 1 and last 1 from B frame / P frame) ?
Regards,
Alex
Nhat Huy wrote:
On Thu, Sep 9, 2010 at 9:00 PM, Alex Grosu <[email protected]> wrote:
Hello Huy
Thanks a lot for the answer. I found this solution 2 days ago, but first I
thought it was a dirty one. I wanted to check this before posting here
again, but you took it ahead. Your pointing shows me that in fact this is
not a dirty solution, so thanks a lot for support.
So, what I had to do (as Huy suggested), was to couple 7 8 and 5 NAL types
into only one buffer and to present it to libavcodec (in
avcodec_decode_video2 function).
Thus, using the [ and ] characters to delimit buffer boundaries, I was
coupling following before send them to libavcodec:
[7 8 5] [1] [1] [1] [1] [7 8 5] [1] [1] [1] and so on.
I don't receive errors anymore. Everything works now
Thank you
Nhat Huy wrote:
On Thu, Sep 2, 2010 at 3:58 PM, Alex Grosu <[email protected]> wrote:
Hello
I am currently decoding h264 streams (with libavcodec) and I am stuck
with
the logic for SPS (sequence parameter set) and PPS (picture parameter
set).
The board from which I am receiving the packages is sending a NAL unit in
each packet. The sequence for NAL types is:
7(SPS) 8(PPS) 5 1 1 1 1 7 8 5 1 1 1...
I am putting in front of each NAL the start sequence 0x000001 and sending
this packet to avcodec_decode_video2. When 7 and 8 types are coming, I am
doing the same logic, but avcodec_decode_video2 is returning -1. After
this,
all the received NALs are decoded and the images are displayed. Every
time
when SPS and PPS are coming, avcodec_decode_video2 returns -1 (fails). I
searched all over the net , and I still can't understand how to fill up
the
extradata and extradata_size from AVCodecContext used. All I found is
this
link: http://www.mail-archive.com/[email protected]/msg04939.html.
As I saw from here:
"To decode H.264 stream you need to have SPS and PPS NAL units also .".
Ok,
I have them, but frankly I don't know how to use them. At first, I
thought
that avcodec_decode_video2 will "automatically" use them. But returning
-1,
I don't see how. Also, If I am discarding SPS and PPS from sending them
to
libavcodec, nothing is decoded anymore.
Can you please give me a hint?
Thank you a lot !
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Hi,
I think you should read H.264 bit stream structure and use these tools to
analyze a NAL unit of H.264 bitstream.
http://www.codecian.com/
http://tsviatko.jongov.com/index_prj_h264videoesviewer.htm
When FFmpeg decode a NAL unit, if the nal_unit_type equal 7,8 it will
continue decode to find the IDR nal_unit. In your case, I think that
FFmpeg
found SPS, PPS but it can not find IDR thus it returns -1.
Hope it helps.
Huy.
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Hi,
If you coupled H.264 slice as [7 8 5] [1] [1] [1] [1] [7 8 5] [1] [1] [1]
and so on, it can work well only in single slice/ frame case.
If you use multiple slice , it goes wrong.
For ex. my sequence has 5 frame I B B B P, and number of slices is 4 per
frame. The NAL_unit_type of bit stream is:
[7 8 5 5 5 5][1 1 1 1][1 1 1 1][1 1 1 1][1 1 1 1]
I use [ and ] to mark the frame boundary.
When you feed avcodec_decode_video2, the input buffer must contains whole
frame data.
Thus, the problem that you have to calculate exactly the input buffer
length, and feed it enough data plus some padding if necessary before pass
it to avcodec_decode_video2.
Huy.
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