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)
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 */
s->buf_ptr = s->buffer + offset1;
} else if ((!s->seekable ||
- offset1 <= s->buf_end + s->short_seek_threshold - s->buffer) &&
+ offset1 <= buffer_size + s->short_seek_threshold) &&
!s->write_flag && offset1 >= 0 &&
(!s->direct || !s->seek) &&
(whence != SEEK_END || force)) {
fill_buffer(s);
if (s->eof_reached)
return AVERROR_EOF;
- s->buf_ptr = s->buf_end + offset - s->pos;
+ s->buf_ptr = s->buf_end - (s->pos - offset);
} else if(!s->write_flag && offset1 < 0 && -offset1 < buffer_size>>1 && s->seek && offset > 0) {
int64_t res;
size1 = size;
while (size > 0) {
- len = s->buf_end - s->buf_ptr;
- if (len > size)
- len = size;
+ len = FFMIN(s->buf_end - s->buf_ptr, 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) {
/* do not modify buffer if EOF reached so that a seek back can
be done without rereading data */
s->bytes_read += len;
size -= len;
buf += len;
+ // reset the buffer
s->buf_ptr = s->buffer;
s->buf_end = s->buffer/* + len*/;
}