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avformat/aviobuf: Improve readability of aviobuf (Add comments and docs)

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Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Bryan Huh 2015-11-15 18:02:11 -08:00 committed by Michael Niedermayer
parent c9944f7596
commit a01c24e8c5
2 changed files with 52 additions and 2 deletions
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47
libavformat/avio.h
View File

@ -122,6 +122,53 @@ typedef struct AVIOContext {
* to any av_opt_* functions in that case.
*/
const AVClass *av_class;
/*
* The following shows the relationship between buffer, buf_ptr, buf_end, buf_size,
* and pos, when reading and when writing (since AVIOContext is used for both):
*
**********************************************************************************
* READING
**********************************************************************************
*
* | buffer_size |
* |---------------------------------------|
* | |
*
* buffer buf_ptr buf_end
* +---------------+-----------------------+
* |/ / / / / / / /|/ / / / / / /| |
* read buffer: |/ / consumed / | to be read /| |
* |/ / / / / / / /|/ / / / / / /| |
* +---------------+-----------------------+
*
* pos
* +-------------------------------------------+-----------------+
* input file: | | |
* +-------------------------------------------+-----------------+
*
*
**********************************************************************************
* WRITING
**********************************************************************************
*
* | buffer_size |
* |-------------------------------|
* | |
*
* buffer buf_ptr buf_end
* +-------------------+-----------+
* |/ / / / / / / / / /| |
* write buffer: | / to be flushed / | |
* |/ / / / / / / / / /| |
* +-------------------+-----------+
*
* pos
* +--------------------------+-----------------------------------+
* output file: | | |
* +--------------------------+-----------------------------------+
*
*/
unsigned char *buffer; /**< Start of the buffer. */
int buffer_size; /**< Maximum buffer size */
unsigned char *buf_ptr; /**< Current position in the buffer */

7
libavformat/aviobuf.c
View File

@ -213,6 +213,7 @@ int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
return AVERROR(EINVAL);
buffer_size = s->buf_end - s->buffer;
// pos is the absolute position that the beginning of s->buffer corresponds to in the file
pos = s->pos - (s->write_flag ? 0 : buffer_size);
if (whence != SEEK_CUR && whence != SEEK_SET)
@ -227,7 +228,7 @@ int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
if (offset < 0)
return AVERROR(EINVAL);
offset1 = offset - pos;
offset1 = offset - pos; // "offset1" is the relative offset from the beginning of s->buffer
if (!s->must_flush && (!s->direct || !s->seek) &&
offset1 >= 0 && offset1 <= buffer_size - s->write_flag) {
/* can do the seek inside the buffer */
@ -545,7 +546,8 @@ int avio_read(AVIOContext *s, unsigned char *buf, int size)
if (len > size)
len = size;
if (len == 0 || s->write_flag) {
if((s->direct || size > s->buffer_size) && !s->update_checksum){
if((s->direct || size > s->buffer_size) && !s->update_checksum) {
// bypass the buffer and read data directly into buf
if(s->read_packet)
len = s->read_packet(s->opaque, buf, size);
if (len <= 0) {
@ -560,6 +562,7 @@ int avio_read(AVIOContext *s, unsigned char *buf, int size)
s->bytes_read += len;
size -= len;
buf += len;
// reset the buffer
s->buf_ptr = s->buffer;
s->buf_end = s->buffer/* + len*/;
}