int avio_read(AVIOContext *s, unsigned char *buf, int size) { int len, size1; size1 = size; while (size > 0) { 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) { // bypass the buffer and read data directly into buf if(s->read_packet) len = s->read_packet(s->opaque, buf, size); else len = AVERROR_EOF; if (len == AVERROR_EOF) { /* do not modify buffer if EOF reached so that a seek back can be done without rereading data */ s->eof_reached = 1; break; } else if (len < 0) { s->eof_reached = 1; s->error= len; break; } else { s->pos += len; s->bytes_read += len; size -= len; buf += len; // reset the buffer s->buf_ptr = s->buffer; s->buf_end = s->buffer/* + len*/; } } else { fill_buffer(s); len = s->buf_end - s->buf_ptr; if (len == 0) break; } } else { memcpy(buf, s->buf_ptr, len); buf += len; s->buf_ptr += len; size -= len; } } if (size1 == size) { if (s->error) return s->error; if (avio_feof(s)) return AVERROR_EOF; } return size1 - size; }