[FFmpeg-devel] [PATCH 4/5] avformat/segafilmenc: use ff_format_shift_data for shifting

[Andreas Rheinhardt]

Marton Balint:
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  libavformat/segafilmenc.c | 51 ++++-----------------------------------
>  1 file changed, 5 insertions(+), 46 deletions(-)
> 
> diff --git a/libavformat/segafilmenc.c b/libavformat/segafilmenc.c
> index ff8cb66aca..737805faa6 100644
> --- a/libavformat/segafilmenc.c
> +++ b/libavformat/segafilmenc.c
> @@ -170,54 +170,13 @@ static int film_init(AVFormatContext *format_context)
>  static int write_header(AVFormatContext *format_context, uint8_t *header,
>                          unsigned header_size)
>  {
> -    int ret = 0;
> -    int64_t pos, pos_end;
> -    uint8_t *buf, *read_buf[2];
> -    int read_buf_id = 0;
> -    int read_size[2];
> -    AVIOContext *read_pb;
> -
> -    buf = av_malloc(header_size);
> -    if (!buf)
> -        return AVERROR(ENOMEM);
> -    read_buf[0] = buf;
> -    read_buf[1]  = header;
> -    read_size[1] = header_size;
> -
> -    /* Write the header at the beginning of the file, shifting all content as necessary;
> -     * based on the approach used by MOV faststart. */
> -    avio_flush(format_context->pb);
> -    ret = format_context->io_open(format_context, &read_pb, format_context->url, AVIO_FLAG_READ, NULL);
> -    if (ret < 0) {
> -        av_log(format_context, AV_LOG_ERROR, "Unable to re-open %s output file to "
> -               "write the header\n", format_context->url);
> -        av_free(buf);
> +    int ret = ff_format_shift_data(format_context, 0, header_size);
> +    if (ret < 0)
>          return ret;
> -    }
>  
> -    /* Mark the end of the shift to up to the last data we are going to write,
> -     * and get ready for writing */
> -    pos_end = avio_tell(format_context->pb) + header_size;
> -    pos = avio_seek(format_context->pb, 0, SEEK_SET);
> -
> -    /* start reading at where the new header will be placed */
> -    avio_seek(read_pb, 0, SEEK_SET);
> -
> -    /* shift data by chunk of at most header_size */
> -    do {
> -        int n;
> -        read_size[read_buf_id] = avio_read(read_pb, read_buf[read_buf_id],
> -                                           header_size);
> -        read_buf_id ^= 1;
> -        n = read_size[read_buf_id];
> -        if (n <= 0)
> -            break;
> -        avio_write(format_context->pb, read_buf[read_buf_id], n);
> -        pos += n;
> -    } while (pos < pos_end);
> -    ff_format_io_close(format_context, &read_pb);
> -
> -    av_free(buf);
> +    avio_seek(format_context->pb, 0, SEEK_SET);

This adds a new seek; this could be easily avoided if
ff_format_shift_data() would be changed to add a buffer parameter which
if != NULL would need to point to a buffer of size equal to shift_size
that is directly written at read_start.

> +    avio_write(format_context->pb, header, header_size);
> +
>      return 0;
>  }
>  
>