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

Luca Abeni lucabe72
Mon Feb 20 09:08:39 CET 2006

Hi Baptiste,

I do not know anything about .mov files and about the MOV muxer, but I think the "codec" part of your patches (x264_avc_nal_encode.patch) might be incorrect:

On Sun, 2006-02-19 at 18:23 +0100, Baptiste COUDURIER wrote: [...]

x264avcnalencode.patch

which encodes nals correctly for AVC and write extradata for avcC atom. BTW, what is AVC? I was under the impression that AVC (Advanced Video Coding) = MPEG4 Part 10 = H.264... So, I cannot understand the "encode nals correctly for AVC" part [...] +static int +avcencodenals(uint8t *buf, int size, x264nalt *nals, int nnal) +{ + uint8t *p = buf; + int i; + + for(i = 0; i < nnal; i++){_ _+ int s, sbe;_ _+ size -= 4; /* nal size length is set to 4 in movwriteavcc */_ _+ p += 4; /* advance to stock size */_ _+ s = x264nalencode(p, &size, 0, nals + i);_ _..._ _static int_ _encodenals(uint8t *buf, int size, x264nalt *nals, int nnal)_ _@@ -87,7 +112,10 @@ X264frame(AVCodecContext *ctx, uint8t_ _if(x264encoderencode(x4->enc, &nal, &nnal, &x4->pic, &picout)) return -1; - bufsize = encodenals(buf, bufsize, nal, nnal); + if(ctx->flags & CODECFLAGGLOBALHEADER) + bufsize = avcencodenals(buf, bufsize, nal, nnal); + else + bufsize = encodenals(buf, bufsize, nal, nnal); if(bufsize < 0) return -1; This breaks applications using extradata. Why do you need to change the extradata format? I am not really an expert, but I think extradata should be the "global headers", and according to some drafts I read the current content of extradata correctly matches H.264 global headers.

Also, maybe I am wrong, but I was under the impression that CODEC_FLAG_GLOBAL_HEADER should not change the format of the stream, but should simply move "out of band" some parts of the stream (the global headers, in this case). Is this wrong? Can someone of the ffmpeg developers clarify this?

[...]

+ /* pps */ + p += 2; /* advance to stock size */ + s -= 2; + size = x264nalencode(p, &s, 0, &nal[2]); + if (size < 0) + return -1; + /* write size */ + p -= 2; + sizebe = BE16(&size); In any case, if the patch is committed this "p += 2; .... p -= 2;" thing should be avoided (maybe something like x264_nal_encode(p+2, &s, 0, &nal[2]);... memcpy(p, &size_be, 2); p += size + 2;...)

Moreover, I think you are opencoding the for() loop on the NALs... Why? Also, it seems that you are not putting the first NAL in the extradata?

Again, I apologize if I am misunderstanding something, but my impression is that your patch does at codec level something that should be done at format level... I see "avcC" cited in your libavcodec/x264.c patch, but I think it really is a MOV thing? Or am I wrong?

            Luca

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