Re: [FFmpeg-devel] [PATCH 2/5] avformat/movenc: factorize data shifting

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Marton Balint:
> And move data shift function from movenc to utils.
> 
> Signed-off-by: Marton Balint <cus@passwd.hu>
> ---
>  libavformat/internal.h |  7 ++++++
>  libavformat/movenc.c   | 55 ++---------------------------------------
>  libavformat/utils.c    | 56 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 65 insertions(+), 53 deletions(-)
> 
> diff --git a/libavformat/internal.h b/libavformat/internal.h
> index 2ba795d669..63235ce5cf 100644
> --- a/libavformat/internal.h
> +++ b/libavformat/internal.h
> @@ -1019,4 +1019,11 @@ void ff_format_set_url(AVFormatContext *s, char *url);
>  
>  void avpriv_register_devices(const AVOutputFormat * const o[], const AVInputFormat * const i[]);
>  
> +/**
> + * Make shift_size amount of space at read_start by shifting data in the output
> + * at read_start until the current IO position. The underlying IO context must
> + * be seekable.
> + */
> +int ff_format_shift_data(AVFormatContext *s, int64_t read_start, int shift_size);
> +
>  #endif /* AVFORMAT_INTERNAL_H */
> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> index 0f912dd012..40ad4f8642 100644
> --- a/libavformat/movenc.c
> +++ b/libavformat/movenc.c
> @@ -7150,13 +7150,8 @@ static int compute_sidx_size(AVFormatContext *s)
>  
>  static int shift_data(AVFormatContext *s)
>  {
> -    int ret = 0, moov_size;
> +    int moov_size;
>      MOVMuxContext *mov = s->priv_data;
> -    int64_t pos, pos_end;
> -    uint8_t *buf, *read_buf[2];
> -    int read_buf_id = 0;
> -    int read_size[2];
> -    AVIOContext *read_pb;
>  
>      if (mov->flags & FF_MOV_FLAG_FRAGMENT)
>          moov_size = compute_sidx_size(s);
> @@ -7165,53 +7160,7 @@ static int shift_data(AVFormatContext *s)
>      if (moov_size < 0)
>          return moov_size;
>  
> -    buf = av_malloc(moov_size * 2);
> -    if (!buf)
> -        return AVERROR(ENOMEM);
> -    read_buf[0] = buf;
> -    read_buf[1] = buf + moov_size;
> -
> -    /* Shift the data: the AVIO context of the output can only be used for
> -     * writing, so we re-open the same output, but for reading. It also avoids
> -     * a read/seek/write/seek back and forth. */
> -    avio_flush(s->pb);
> -    ret = s->io_open(s, &read_pb, s->url, AVIO_FLAG_READ, NULL);
> -    if (ret < 0) {
> -        av_log(s, AV_LOG_ERROR, "Unable to re-open %s output file for "
> -               "the second pass (faststart)\n", s->url);
> -        goto end;
> -    }
> -
> -    /* mark the end of the shift to up to the last data we wrote, and get ready
> -     * for writing */
> -    pos_end = avio_tell(s->pb);
> -    avio_seek(s->pb, mov->reserved_header_pos + moov_size, SEEK_SET);
> -
> -    /* start reading at where the new moov will be placed */
> -    avio_seek(read_pb, mov->reserved_header_pos, SEEK_SET);
> -    pos = avio_tell(read_pb);
> -
> -#define READ_BLOCK do {                                                             \
> -    read_size[read_buf_id] = avio_read(read_pb, read_buf[read_buf_id], moov_size);  \
> -    read_buf_id ^= 1;                                                               \
> -} while (0)
> -
> -    /* shift data by chunk of at most moov_size */
> -    READ_BLOCK;
> -    do {
> -        int n;
> -        READ_BLOCK;
> -        n = read_size[read_buf_id];
> -        if (n <= 0)
> -            break;
> -        avio_write(s->pb, read_buf[read_buf_id], n);
> -        pos += n;
> -    } while (pos < pos_end);
> -    ff_format_io_close(s, &read_pb);
> -
> -end:
> -    av_free(buf);
> -    return ret;
> +    return ff_format_shift_data(s, mov->reserved_header_pos, moov_size);
>  }
>  
>  static int mov_write_trailer(AVFormatContext *s)
> diff --git a/libavformat/utils.c b/libavformat/utils.c
> index 332ba534d2..a78797ef57 100644
> --- a/libavformat/utils.c
> +++ b/libavformat/utils.c
> @@ -2035,3 +2035,59 @@ const char *av_disposition_to_string(int disposition)
>  
>      return NULL;
>  }
> +
> +int ff_format_shift_data(AVFormatContext *s, int64_t read_start, int shift_size)
> +{
> +    int ret;
> +    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_array(shift_size, 2);
> +    if (!buf)
> +        return AVERROR(ENOMEM);
> +    read_buf[0] = buf;
> +    read_buf[1] = buf + shift_size;
> +
> +    /* Shift the data: the AVIO context of the output can only be used for
> +     * writing, so we re-open the same output, but for reading. It also avoids
> +     * a read/seek/write/seek back and forth. */
> +    avio_flush(s->pb);
> +    ret = s->io_open(s, &read_pb, s->url, AVIO_FLAG_READ, NULL);
> +    if (ret < 0) {
> +        av_log(s, AV_LOG_ERROR, "Unable to re-open %s output file for shifting data\n", s->url);
> +        goto end;
> +    }
> +
> +    /* mark the end of the shift to up to the last data we wrote, and get ready
> +     * for writing */
> +    pos_end = avio_tell(s->pb);
> +    avio_seek(s->pb, read_start + shift_size, SEEK_SET);
> +
> +    avio_seek(read_pb, read_start, SEEK_SET);
> +    pos = avio_tell(read_pb);

This avio_tell() is redundant: avio_seek() returns the new position on
non-error and in this case it is equal to read_start.

> +
> +#define READ_BLOCK do {                                                             \
> +    read_size[read_buf_id] = avio_read(read_pb, read_buf[read_buf_id], shift_size);  \
> +    read_buf_id ^= 1;                                                               \
> +} while (0)
> +
> +    /* shift data by chunk of at most shift_size */
> +    READ_BLOCK;
> +    do {
> +        int n;
> +        READ_BLOCK;
> +        n = read_size[read_buf_id];
> +        if (n <= 0)
> +            break;
> +        avio_write(s->pb, read_buf[read_buf_id], n);
> +        pos += n;
> +    } while (pos < pos_end);
> +    ff_format_io_close(s, &read_pb);
> +
> +end:
> +    av_free(buf);
> +    return ret;
> +}
> 

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