Hello,
I have several problem when I want to decode a H264 video send by
RTP.
I'm using libavcodec to decode video but I build my own SDP
parser.
If you have time, can you tell me where is the problem in my
method.
I create a structure to store SDP data :
typedef struct{
int packetization_mode;
uint8_t profile_idc;
uint8_t profile_iop;
uint8_t level_idc;
int extradata_size;
uint8_t* extradata;
int width;
int height;
} H264CONTEXT;
H264CONTEXT h264context;
I parse the fmtp line of SDP as the function of ffmpeg
sdp_parse_fmtp_config_h264
Then I found :
level_idc= 41 (base 10)
profile_idc= 66 (base 10)
extradata_size=30
I store 00 00 01 67 42 00 1e e2 90 16 02 4d 81
27 05 01 05 e1 e2 44 54 00 00 01 68 ce 3c 80 00 00 in extradata
* I initialize CodecContext
codecContext->level = h264context.level_idc;
codecContext->profile = h264context.profile_idc;
codecContext->extradata_size=
h264context.extradata_size;
codecContext->extradata =h264context.extradata;
codecContext->hurry_up = 1;
codecContext->debug = 1;
codecContext->stream_codec_tag = 462h;
//0x31637661;
codecContext->flags |= CODEC_FLAG_4MV;
codecContext->flags |= CODEC_FLAG_PART;
codecContext->flags |=CODEC_FLAG_TRUNCATED;
codecContext->flags2 |= CODEC_FLAG2_CHUNKS;
codecContext->error_recognition = 1;
codecContext->error_concealment =
FF_EC_GUESS_MVS;
codecContext->skip_top = 0;
codecContext->skip_bottom = 0;
codecContext->skip_loop_filter = AVDISCARD_NONE;
codecContext->skip_idct =
AVDISCARD_NONE;
codecContext->skip_frame = AVDISCARD_NONE
codecContext->workaround_bugs = 1;
codecContext->codec_type = CODEC_TYPE_VIDEO;
codecContext->codec_id = CODEC_ID_H264;
codecContext->pix_fmt = PIX_FMT_YUV420P;
codecContext->sample_fmt = SAMPLE_FMT_S16;
codecContext->codec_tag =
avcodec_pix_fmt_to_codec_tag (codecContext->pix_fmt ) ;
codecContext->width = 768;
codecContext->height = 576;
I try decode IDR frame.
My IDR frame (nal_type = 5) are fragmented : fragment_type=28
I find in a forum this method :
If the NAL is 28 (1C) then it means that following payload
represents one H264 IDR (I-Frame)
fragment and that I need to collect all of them to
reconstruct H264 IDR (I-Frame).
Fragment that has START BIT = 1:
First byte: [ 3 NAL UNIT BITS | 5 FRAGMENT TYPE BITS]
Second byte: [ START BIT | RESERVED BIT | END BIT | 5 NAL UNIT
BITS]
Other bytes: [... IDR FRAGMENT DATA...]
Other fragments:
First byte: [ 3 NAL UNIT BITS | 5 FRAGMENT TYPE BITS]
Other bytes: [... IDR FRAGMENT DATA...]
To reconstruct IDR I collect this info:
int fragment_type = Data[0] & 0x1F;
int nal_type = Data[1] & 0x1F;
int start_bit = Data[1] & 0x80;
int end_bit = Data[1] & 0x40;
If fragment_type == 28 then payload following it is one
fragment of IDR. Next check is start_bit set,
if it is, then that fragment is the first one in a sequence. I
use it to reconstruct IDR's NAL byte by taking
the first 3 bits from first payload byte (3 NAL UNIT BITS) and
combine them with last 5 bits from
second payload byte (5 NAL UNIT BITS) so I would get a byte
like this
[3 NAL UNIT BITS | 5 NAL UNIT BITS]. Then I write that NAL
byte first
into a clear buffer with all other following bytes from that
fragment. Remember to skip first byte
in a sequence since it is not a part of IDR, but only
identifies the fragment.
If start_bit and end_bit are 0 then I just write the payload
(skipping first
payload byte that identifies the fragment) to the buffer.
If start_bit is 0 and end_bit is 1, that means that it is the
last fragment,
and I just write its payload (skipping the first byte that
identifies the fragment)
to the buffer, and now I have my IDR reconstructed.
Then I send my IDR to decoder but I some error occurs :
pps_id (32) out of range
illegal POC type 5
it think is due SPS/PPS setting but I don't understant why
Thx
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