Hi,
Morfsta schrieb:
> It seems that you must start scanning the mpeg stream for a Sequence
> Parameter Set with a NAL Access Code of 7. At first glance this
> doesn't appear too bad, as the code is already in
> src/demuxers/demux_mpeg_pes.c to scan for a NAL code of 9 (Access Unit
> Delimiter), which it uses to detect the presence of H264 stream.
Correct.
> I thought it would be quite straightforward to find the NAL code of 7
> and then parse the SPS and in turn find the height and width
> parameters. However, trying to get this to work in sequence is not
> that easy as the parse_video_stream seems to want to identify MPEG1/2
> or H264 and then just init the decoders. This is where the
> initialisation of CoreAVCDecoder.ax is made, currently with the
> hardcoded video size of 1920x1080. What I want it to do is identify
> the H264 stream and then keep scanning for an SPS to identify the size
> prior to initting the decoder.
>
> It seems that once it's found the AUD it doesn't really want to keep
> looking for a SPS. I tried modifying the code to look for a SPS to
> init the H264 sequence, however haven't had much success with that
> either.
Typically, a SPS is found in the same memory block which starts
with an AUD for an "I frame". From VDR's remux.c,
cRemux::ScanVideoPacket():
if (!p[-2] && !p[-1]) { // found 0x000001
if (h264) {
int nal_unit_type = p[1] & 0x1F;
switch (nal_unit_type) {
case 9: { // access unit delimiter
int primary_pic_type = p[2] >> 5;
switch (primary_pic_type) {
case 0: // I
case 3: // SI
case 5: // I, SI
PictureType = I_FRAME;
break;
> It might be the case that the whole initialisation of the CoreAVC
> decoder would be better suited somewhere else in the code.... :-\
Doesn't the decoder support a callback function where it tells
you, the detected frame size? It'll really be a mess to do H.264
"decoding" in the demuxer.
Bye.
--
Dipl.-Inform. (FH) Reinhard Nissl
mailto:rnissl@xxxxxx
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