[MPlayer-users] Gxf file format

[Reimar Döffinger]

Hi,
On Thu, Aug 18, 2005 at 05:42:44PM +0200, Sebastian Sch?fer wrote:
>         61.494.832 THX_Science_FLT_1920.302

Uncompressed PCM with a bit of additional overhead. But most annoying is
the really weird bit order (little endian, but every byte in reverse
order and the highest nibble is used for flags, yuck).
I attached a decoder for this format, but be aware that the output is
not necessarily correct, I determined the order of the bits purely via
statistics (counting how often the bit flips without more than 10 others
flipping - the higher the count, the less significant the bit - the
"without more than 10 others flipping" is necessary because it is a
signed format).
Probably no chance of supporting it in MPlayer natively though, since
there is no way to autodetect this as far as I can see.
Well, maybe extension based detection in libavformat? Somebody
interested in implementing this?

>        239.328.576 THX_Science_FLT_1920.gxf

Hmmm... almost certainly a MPEG-ES container... Not sure about the
contents. Googling tells me probably JPEG2000, but I don't know enough
about JPEG2000 to know. I am quite certain it is neither MPEG1/2/4 nor
MJPEG.

Greetings,
Reimar Döffinger
-------------- next part --------------
#include <stdlib.h>
#include <stdio.h>
#include <inttypes.h>
#include <string.h>
#include <byteswap.h>
#define le2me_32(x) (x)
#define le2me_16(x) (x)
#define be2me_16(x) bswap_16(x)

// From MPlayer libao/ao_pcm.c
#define WAV_ID_RIFF 0x46464952 /* "RIFF" */
#define WAV_ID_WAVE 0x45564157 /* "WAVE" */
#define WAV_ID_FMT  0x20746d66 /* "fmt " */
#define WAV_ID_DATA 0x61746164 /* "data" */
#define WAV_ID_PCM  0x0001

struct WaveHeader {
  uint32_t riff;
  uint32_t file_length;
  uint32_t wave;
  uint32_t fmt;
  uint32_t fmt_length;
  uint16_t fmt_tag;
  uint16_t channels;
  uint32_t sample_rate;
  uint32_t bytes_per_second;
  uint16_t block_align;
  uint16_t bits;
  uint32_t data;
  uint32_t data_length;
};

static struct WaveHeader wavhdr = {
  le2me_32(WAV_ID_RIFF),
  le2me_32(0x7fffffff),
  le2me_32(WAV_ID_WAVE),
  le2me_32(WAV_ID_FMT),
  le2me_32(16),
  le2me_16(WAV_ID_PCM),
  le2me_16(6),
  le2me_32(96000),
  le2me_32(1728000),
  le2me_16(18),
  le2me_16(24),
  le2me_32(WAV_ID_DATA),
  le2me_32(0x7fffffff),
};

// this format is completely braindead, and this bitorder
// is the result of pure guesswork (counting how often
// the bits flip), so it might be wrong.
void fixup(unsigned char *in_, unsigned char *out) {
  int i;
  unsigned char in[3] = {in_[0], in_[1], in_[2]};
  unsigned char sync = in[2] & 0x0f; // sync flags
  in[2] >>= 4;
  out[2] = 0;
  for (i = 0; i < 4; i++) {
    out[2] <<= 1;
    out[2] |= in[2] & 1;
    in[2] >>= 1;
  }
  for (i = 0; i < 4; i++) {
    out[2] <<= 1;
    out[2] |= in[1] & 1;
    in[1] >>= 1;
  }
  out[1] = 0;
  for (i = 0; i < 4; i++) {
    out[1] <<= 1;
    out[1] |= in[1] & 1;
    in[1] >>= 1;
  }
  for (i = 0; i < 4; i++) {
    out[1] <<= 1;
    out[1] |= in[0] & 1;
    in[0] >>= 1;
  }
  out[0] = 0;
  for (i = 0; i < 4; i++) {
    out[0] <<= 1;
    out[0] |= in[0] & 1;
    in[0] >>= 1;
  }
  out[0] <<= 4;
  out[0] |= sync; // sync flags go into lowest bits
  // it seems those might also contain audio data,
  // don't know if this is the right order then
}

int main(int argc, char *argv[]) {
  FILE *in = fopen(argv[1], "r");
  FILE *out = fopen(argv[2], "w");
  int i;
  uint16_t blocklen, unknown;
  unsigned char *block;
  if (!in) {
    printf("Could not open %s for reading\n", argv[1]);
    return EXIT_FAILURE;
  }
  if (!out) {
    printf("Could not open %s for writing\n", argv[2]);
    return EXIT_FAILURE;
  }
  fwrite(&wavhdr, 1, sizeof(wavhdr), out);
  do {
    fread(&blocklen, 2, 1, in);
    blocklen = be2me_16(blocklen);
    fread(&unknown, 2, 1, in);
    block = malloc(blocklen);
    blocklen = fread(block, 1, blocklen, in);
    for (i = 0; i < blocklen; i += 3)
      fixup(&block[i], &block[i]);
    fwrite(block, 1, blocklen, out);
    free(block);
  } while (!feof(in));
  return EXIT_SUCCESS;
}