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tweak the seeking a little more

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This commit is contained in:
Josh Coalson
2001-04-05 20:11:25 +00:00
parent bbbdba71bc
commit 243a067a58
1 changed files with 24 additions and 20 deletions
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44
src/libFLAC/file_decoder.c
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@@ -388,7 +388,7 @@ void error_callback_(const FLAC__StreamDecoder *decoder, FLAC__StreamDecoderErro
bool seek_to_absolute_sample_(FLAC__FileDecoder *decoder, long filesize, uint64 target_sample) bool seek_to_absolute_sample_(FLAC__FileDecoder *decoder, long filesize, uint64 target_sample)
{ {
long l, r, pos, last_pos = -1; long lower_bound, upper_bound, pos, last_pos = -1;
unsigned approx_bytes_per_frame; unsigned approx_bytes_per_frame;
uint64 last_frame_sample = 0xffffffffffffffff; uint64 last_frame_sample = 0xffffffffffffffff;
bool needs_seek; bool needs_seek;
@@ -396,7 +396,7 @@ bool seek_to_absolute_sample_(FLAC__FileDecoder *decoder, long filesize, uint64
/* we are just guessing here, but we want to guess high, not low */ /* we are just guessing here, but we want to guess high, not low */
if(decoder->guts->stream_info.max_framesize > 0) { if(decoder->guts->stream_info.max_framesize > 0) {
approx_bytes_per_frame = decoder->guts->stream_info.max_framesize + 64; approx_bytes_per_frame = decoder->guts->stream_info.max_framesize;
} }
else if(!is_variable_blocksize_stream) { else if(!is_variable_blocksize_stream) {
/* note there are no () around 'decoder->guts->stream_info.bits_per_sample/8' to keep precision up since it's an integer calulation */ /* note there are no () around 'decoder->guts->stream_info.bits_per_sample/8' to keep precision up since it's an integer calulation */
@@ -407,31 +407,35 @@ bool seek_to_absolute_sample_(FLAC__FileDecoder *decoder, long filesize, uint64
/* The file pointer is currently at the first frame plus any read /* The file pointer is currently at the first frame plus any read
ahead data, so first we get the file pointer, then subtract ahead data, so first we get the file pointer, then subtract
uncomsumed bytes to get the position (l) of the first frame uncomsumed bytes to get the position (lower_bound) of the first frame
in the file */ in the file */
if(-1 == (l = ftell(decoder->guts->file))) { if(-1 == (lower_bound = ftell(decoder->guts->file))) {
decoder->state = FLAC__FILE_DECODER_SEEK_ERROR; decoder->state = FLAC__FILE_DECODER_SEEK_ERROR;
return false; return false;
} }
l -= FLAC__stream_decoder_input_bytes_unconsumed(decoder->guts->stream) + 1; lower_bound -= FLAC__stream_decoder_input_bytes_unconsumed(decoder->guts->stream);
if(l < 0) if(lower_bound < 0)
l = 0; lower_bound = 0;
/* calc the upper_bound, beyond which we never want to seek */
if(decoder->guts->stream_info.max_framesize > 0)
upper_bound = filesize - (decoder->guts->stream_info.max_framesize + 128 + 2); /* 128 for a possible ID3V1 tag, 2 for indexing differences */
else
upper_bound = filesize - ((decoder->guts->stream_info.channels * decoder->guts->stream_info.bits_per_sample * FLAC__MAX_BLOCK_SIZE) / 8 + 128 + 2);
/* Now we need to use the metadata and the filelength to search to the frame with the correct sample */ /* Now we need to use the metadata and the filelength to search to the frame with the correct sample */
#ifdef _MSC_VER #ifdef _MSC_VER
/* with VC++ you have to spoon feed it the casting */ /* with VC++ you have to spoon feed it the casting */
pos = l + (long)((double)(int64)target_sample / (double)(int64)decoder->guts->stream_info.total_samples * (double)(filesize-l+1)) - approx_bytes_per_frame; pos = lower_bound + (long)((double)(int64)target_sample / (double)(int64)decoder->guts->stream_info.total_samples * (double)(filesize-lower_bound-1)) - approx_bytes_per_frame;
#else #else
pos = l + (long)((double)target_sample / (double)decoder->guts->stream_info.total_samples * (double)(filesize-l+1)) - approx_bytes_per_frame; pos = lower_bound + (long)((double)target_sample / (double)decoder->guts->stream_info.total_samples * (double)(filesize-lower_bound-1)) - approx_bytes_per_frame;
#endif #endif
if(decoder->guts->stream_info.max_framesize > 0)
r = filesize - decoder->guts->stream_info.max_framesize - 2; /* clip the position to the bounds, lower bound takes precedence */
else if(pos >= upper_bound)
r = filesize - ((decoder->guts->stream_info.channels * decoder->guts->stream_info.bits_per_sample * FLAC__MAX_BLOCK_SIZE) / 8 + 64); pos = upper_bound-1;
if(pos >= r) if(pos < lower_bound)
pos = r-1; pos = lower_bound;
if(pos < l)
pos = l;
needs_seek = true; needs_seek = true;
decoder->guts->target_sample = target_sample; decoder->guts->target_sample = target_sample;
@@ -468,7 +472,7 @@ bool seek_to_absolute_sample_(FLAC__FileDecoder *decoder, long filesize, uint64
pos -= approx_bytes_per_frame; pos -= approx_bytes_per_frame;
needs_seek = true; needs_seek = true;
} }
else { else { /* target_sample >= this_frame_sample + this frame's blocksize */
last_pos = pos; last_pos = pos;
if(-1 == (pos = ftell(decoder->guts->file))) { if(-1 == (pos = ftell(decoder->guts->file))) {
decoder->state = FLAC__FILE_DECODER_SEEK_ERROR; decoder->state = FLAC__FILE_DECODER_SEEK_ERROR;
@@ -478,8 +482,8 @@ bool seek_to_absolute_sample_(FLAC__FileDecoder *decoder, long filesize, uint64
needs_seek = false; needs_seek = false;
} }
} }
if(pos < l) if(pos < lower_bound)
pos = l; pos = lower_bound;
last_frame_sample = this_frame_sample; last_frame_sample = this_frame_sample;
} }
} }