[Ffmpeg-devel] Re: [PATCH] x264 avc encoding, movenc avcC, ctts (original) (raw)

Stefan Gehrer stefan.gehrer
Mon Feb 20 12:32:27 CET 2006

Luca Abeni wrote:

Hi Baptiste,

On Mon, 2006-02-20 at 10:35 +0100, Baptiste COUDURIER wrote: [...]

The problem is that various containers define their own format for the H.264 extradata.

Yes, I agree. This is why I think that things (extradata, in this case) should be exported by libavcodec in a "format independent way". So, I think the current code in x264.c should not be changed (I might be misreading things, but it seems to me that x264.c is currently producing a stream as described in the "H.264 codec" standard... So, it looks correct).

What formats other than MOV/MP4 use those extradata ? I do not think this is the point; I think the point is that the H.264 codec should output a raw H.264 stream, not something format dependent. (anyway, I use extradata for some H.264 streaming experiments I am doing. My current code can stream NALs without having to know if the CODECFLAGGLOBALHEADER is set or not; with your patch I'd have to write different code for the CODECFLAGGLOBALHEADER case). If libx264 chose to export encoderheaders in AVC format, we would use that, right ? At the cost of showing all my ignorance, I have to admit that I do not see the "AVC format" defined in the MPEG4 Part 10 draft I have here... It seems to me that the format described there is the one produced by the current code. Where is the AVC format defined? I might be mistaken here, but my impression was that in a mp4/mov file one would put what in the H.264 spec is called "RBSP (raw bytestream packet)" syntax. If you put a start code (0x000001) and a byte containing forbidden_zero_bit, nal_ref_idc and nal_unit_type in front of the RBSP and escape all byte sequences 0x0000 as 0x000003, you get what is called a NAL unit. This is what you need to create an ES and therefore you want this in MPEG1/2 systems (ISO 13818-1) stuff.

However, I did not read this up but had that impression after looking at .mov files in a hexeditor and not finding any startcodes. ;)

Regards Stefan Gehrer

More information about the ffmpeg-devel mailing list