[FFmpeg-devel] [PATCH] dnxhd parser and raw de/muxer

[Michael Niedermayer]

On Mon, Sep 08, 2008 at 02:54:14PM -0700, Baptiste Coudurier wrote:
> Hi,
> 
> $subject, to use dnxhd raw essences.
[...]
> Index: libavformat/raw.c
> ===================================================================
> --- libavformat/raw.c	(revision 15275)
> +++ libavformat/raw.c	(working copy)
> @@ -487,6 +487,15 @@
>  }
>  #endif
>  
> +static int dnxhd_probe(AVProbeData *p)
> +{
> +    static const uint8_t header[] = {0x00,0x00,0x02,0x80,0x01};
> +    if (!memcmp(p->buf, header, 5))
> +        return AVPROBE_SCORE_MAX;
> +    else
> +        return 0;
> +}

Can more than that be used for a more reliable probe?
I mean yes its 5 bytes but they are all 0 except 3 bits, thus this might
be more common in real files than expected in random data.

[...]
> +typedef struct {
> +    ParseContext pc;
> +    uint64_t state;
> +} DNXHDParseContext;
> +
> +#define DNXHD_HEADER_PREFIX 0x0000028001
> +
> +static int dnxhd_find_frame_end(DNXHDParseContext *ctx, const uint8_t *buf,
> +                                int buf_size)
> +{
> +    uint64_t state = ctx->state;
> +    int pic_found = ctx->pc.frame_start_found;
> +    int i = 0;
> +
> +    if(!pic_found){
> +        for(i = 0; i < buf_size; i++) {
> +            state = (state<<8) | buf[i];
> +            if((state & 0xffffffffffLL) == DNXHD_HEADER_PREFIX){
> +                i++;
> +                pic_found = 1;
> +                break;
> +            }
> +        }
> +    }
> +
> +    if(pic_found){
> +        /* EOF considered as end of frame */
> +        if (!buf_size)
> +            return 0;
> +        for(; i < buf_size; i++){
> +            state = (state<<8) | buf[i];
> +            if((state & 0xffffffffffLL) == DNXHD_HEADER_PREFIX){
> +                ctx->pc.frame_start_found=0;
> +                ctx->state=-1;
> +                return i-4;
> +            }
> +        }
> +    }
> +    ctx->pc.frame_start_found = pic_found;
> +    ctx->state = state;
> +    return END_NOT_FOUND;
> +}
> +
> +static int dnxhd_parse(AVCodecParserContext *s,
> +                           AVCodecContext *avctx,
> +                           const uint8_t **poutbuf, int *poutbuf_size,
> +                           const uint8_t *buf, int buf_size)
> +{
> +    DNXHDParseContext *ctx = s->priv_data;
> +    int next;
> +
> +    if(s->flags & PARSER_FLAG_COMPLETE_FRAMES){
> +        next= buf_size;
> +    }else{
> +        next= dnxhd_find_frame_end(ctx, buf, buf_size);
> +        if(ff_combine_frame(&ctx->pc, next, &buf, &buf_size) < 0){
> +            *poutbuf = NULL;
> +            *poutbuf_size = 0;
> +            return buf_size;
> +        }
> +    }
> +    *poutbuf = buf;
> +    *poutbuf_size = buf_size;
> +    return next;
> +}

Iam not sure if this is correct, ff_combine_frame() upates state, but
thats just its 32bit state, it has no knowledge of the 64bit state.
This should lead to problems when DNXHD_HEADER_PREFIX is split accross
2 input frames.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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