[FFmpeg-devel] Added support for XV video files

[Michael Niedermayer]

On Sun, Mar 24, 2019 at 04:35:40PM +0530, Shivam Goyal wrote:
> The attached patch is for ticket #3720
> 
>     https://trac.ffmpeg.org/ticket/3720
> 
> I have tested this demuxer on the files 1.xv and 5.xv attached with the
> ticket
> 
> http://samples.ffmpeg.org/ffmpeg-bugs/trac/ticket3720/
> 
> 
>  It is working on both of these files.
> 
> As XV video files are flv files with some encrypted data. These can be
> converted to flv without loosing video quality (and it would be really
> fast). I have also tried this and it is working "ffmpeg -i 1.xv -c copy
> converted.flv".
> 
> 
> Please suggest any improvements
> 
> 
[...]

> diff --git a/libavformat/xvtools.h b/libavformat/xvtools.h
> new file mode 100644
> index 0000000000..42c2c65c46
> --- /dev/null
> +++ b/libavformat/xvtools.h
> @@ -0,0 +1,95 @@

> +int flvid = 0x46;
> +
> +
> +int byte_shift(int byte,int shift);
> +int find_rot(AVIOContext *pb);
> +int xvio_r8(AVIOContext *pb, int rot);
> +unsigned int xvio_rb16(AVIOContext *s, int rot);
> +unsigned int xvio_rb24(AVIOContext *s, int rot);
> +unsigned int xvio_rb32(AVIOContext *s, int rot);
> +uint64_t xvio_rb64(AVIOContext *s, int rot);
> +int xv_string_decrypt(int64_t curr_pos, char *buffer, int length, int rot);
> +
> +
> +
> +int byte_shift(int byte,int shift){
> +    return ((byte + shift)&0xff);
> +}
> +
> +
> +int find_rot(AVIOContext *pb){
> +    int64_t curr_pos = avio_tell(pb);
> +    avio_seek(pb,0x200000,SEEK_SET);
> +    int rot = flvid - avio_r8(pb);
> +    avio_seek(pb,curr_pos, SEEK_SET);
> +    return rot;
> +}
> +
> +
> +
> +int xvio_r8(AVIOContext *pb, int rot){
> +    int64_t curr_pos = avio_tell(pb);
> +    if(curr_pos < 0x200400){
> +        int ret=avio_r8(pb);
> +        if(ret == 0)return 0;
> +        ret = byte_shift(ret,rot);
> +        return ret;
> +    }
> +    int ret=avio_r8(pb);
> +    return ret;
> +}

There is so much wrong with this code
global variables are not ok in a demuxer that can have multiple instances
global variables do not belong in headers either
also non static inline functions do not belong in headers

this xvio stuff all looks like a bad idea.
Do i guess correctly that this fileformat is flv but scrambled at the IO
layer ?
if this is true it may be possible to implement a xv demuxer as a
descrambler which than passes the data on to a unchanged flv demuxer.
If that how this xv fundamentally works then that would be much
cleaner.
Also theflv demuxer duplication is not ok



> +
> +
> +unsigned int xvio_rb16(AVIOContext *s, int rot)
> +{
> +    unsigned int val;
> +    val = xvio_r8(s, rot) << 8;
> +    val |= xvio_r8(s, rot);
> +    return val;
> +}
> +
> +
> +unsigned int xvio_rb24(AVIOContext *s, int rot)
> +{
> +    unsigned int val;
> +    val = xvio_rb16(s, rot) << 8;
> +    val |= xvio_r8(s, rot);
> +    return val;
> +}
> +
> +
> +unsigned int xvio_rb32(AVIOContext *s, int rot)
> +{
> +    unsigned int val;
> +    val = xvio_rb16(s, rot) << 16;
> +    val |= xvio_rb16(s, rot);
> +    return val;
> +}
> +
> +
> +uint64_t xvio_rb64(AVIOContext *s, int rot)
> +{
> +    uint64_t val;
> +    val = (uint64_t)xvio_rb32(s, rot) << 32;
> +    val |= (uint64_t)xvio_rb32(s, rot);
> +    return val;
> +}
> +
> +
> +
> +int xv_string_decrypt(int64_t curr_pos, char *buffer, int length, int rot){
> +    if(curr_pos>=0x200400){
> +        return 0;
> +    }
> +    for(int i=0;i<length;i++){
> +        if((curr_pos+i) < 0x200400){
> +            buffer[i] = byte_shift(buffer[i],rot);
> +        }
> +        else{
> +            break;
> +        }
> +    }
> +    return 0;
> +}
> +
> +
> -- 
> 2.21.0
> 

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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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