[FFmpeg-devel] [PATCH 2/3] lavf/webm_dash: Fix incorrect bandwidth computation

[Vignesh Venkatasubramanian]

On Wed, Oct 1, 2014 at 10:13 AM, Vignesh Venkatasubramanian
<vigneshv at google.com> wrote:
> Fix incorrect bandwidth computation in some cases. When the cue end
> descriptor is null (i.e.) start_time_ns == -1, existing bandwidth
> computed (if any) should be returned rather than returning 0.
>
> Signed-off-by: Vignesh Venkatasubramanian <vigneshv at google.com>
> ---
>  libavformat/matroskadec.c | 96 ++++++++++++++++++++++++-----------------------
>  1 file changed, 49 insertions(+), 47 deletions(-)
>
> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> index d856fcc..0e405c7 100644
> --- a/libavformat/matroskadec.c
> +++ b/libavformat/matroskadec.c
> @@ -3188,55 +3188,57 @@ static int64_t webm_dash_manifest_compute_bandwidth(AVFormatContext *s, int64_t
>          }
>          if (desc_end.start_time_ns == -1) {
>              // The prebuffer is larger than the duration.
> -            return (matroska->duration * matroska->time_scale >= prebuffered_ns) ? -1 : 0;
> -        }
> -
> -        // The prebuffer ends in the last Cue. Estimate how much data was
> -        // prebuffered.
> -        pre_bytes = desc_end.end_offset - desc_end.start_offset;
> -        pre_ns = desc_end.end_time_ns - desc_end.start_time_ns;
> -        pre_sec = pre_ns / nano_seconds_per_second;
> -        prebuffer_bytes +=
> -            pre_bytes * ((temp_prebuffer_ns / nano_seconds_per_second) / pre_sec);
> -
> -        prebuffer = prebuffer_ns / nano_seconds_per_second;
> -
> -        // Set this to 0.0 in case our prebuffer buffers the entire video.
> -        bits_per_second = 0.0;
> -        do {
> -            int64_t desc_bytes = desc_end.end_offset - desc_beg.start_offset;
> -            int64_t desc_ns = desc_end.end_time_ns - desc_beg.start_time_ns;
> -            double desc_sec = desc_ns / nano_seconds_per_second;
> -            double calc_bits_per_second = (desc_bytes * 8) / desc_sec;
> -
> -            // Drop the bps by the percentage of bytes buffered.
> -            double percent = (desc_bytes - prebuffer_bytes) / desc_bytes;
> -            double mod_bits_per_second = calc_bits_per_second * percent;
> -
> -            if (prebuffer < desc_sec) {
> -                double search_sec =
> -                    (double)(matroska->duration * matroska->time_scale) / nano_seconds_per_second;
> -
> -                // Add 1 so the bits per second should be a little bit greater than file
> -                // datarate.
> -                int64_t bps = (int64_t)(mod_bits_per_second) + 1;
> -                const double min_buffer = 0.0;
> -                double buffer = prebuffer;
> -                double sec_to_download = 0.0;
> -
> -                int rv = buffer_size_after_time_downloaded(prebuffered_ns, search_sec, bps,
> -                                                           min_buffer, &buffer, &sec_to_download,
> -                                                           s, cues_start);
> -                if (rv < 0) {
> -                    return -1;
> -                } else if (rv == 0) {
> -                    bits_per_second = (double)(bps);
> -                    break;
> +            if (matroska->duration * matroska->time_scale >= prebuffered_ns)
> +              return -1;
> +            bits_per_second = 0.0;
> +        } else {
> +            // The prebuffer ends in the last Cue. Estimate how much data was
> +            // prebuffered.
> +            pre_bytes = desc_end.end_offset - desc_end.start_offset;
> +            pre_ns = desc_end.end_time_ns - desc_end.start_time_ns;
> +            pre_sec = pre_ns / nano_seconds_per_second;
> +            prebuffer_bytes +=
> +                pre_bytes * ((temp_prebuffer_ns / nano_seconds_per_second) / pre_sec);
> +
> +            prebuffer = prebuffer_ns / nano_seconds_per_second;
> +
> +            // Set this to 0.0 in case our prebuffer buffers the entire video.
> +            bits_per_second = 0.0;
> +            do {
> +                int64_t desc_bytes = desc_end.end_offset - desc_beg.start_offset;
> +                int64_t desc_ns = desc_end.end_time_ns - desc_beg.start_time_ns;
> +                double desc_sec = desc_ns / nano_seconds_per_second;
> +                double calc_bits_per_second = (desc_bytes * 8) / desc_sec;
> +
> +                // Drop the bps by the percentage of bytes buffered.
> +                double percent = (desc_bytes - prebuffer_bytes) / desc_bytes;
> +                double mod_bits_per_second = calc_bits_per_second * percent;
> +
> +                if (prebuffer < desc_sec) {
> +                    double search_sec =
> +                        (double)(matroska->duration * matroska->time_scale) / nano_seconds_per_second;
> +
> +                    // Add 1 so the bits per second should be a little bit greater than file
> +                    // datarate.
> +                    int64_t bps = (int64_t)(mod_bits_per_second) + 1;
> +                    const double min_buffer = 0.0;
> +                    double buffer = prebuffer;
> +                    double sec_to_download = 0.0;
> +
> +                    int rv = buffer_size_after_time_downloaded(prebuffered_ns, search_sec, bps,
> +                                                               min_buffer, &buffer, &sec_to_download,
> +                                                               s, cues_start);
> +                    if (rv < 0) {
> +                        return -1;
> +                    } else if (rv == 0) {
> +                        bits_per_second = (double)(bps);
> +                        break;
> +                    }
>                  }
> -            }
>
> -            desc_end = get_cue_desc(s, desc_end.end_time_ns, cues_start);
> -        } while (desc_end.start_time_ns != -1);
> +                desc_end = get_cue_desc(s, desc_end.end_time_ns, cues_start);
> +            } while (desc_end.start_time_ns != -1);
> +        }
>          if (bandwidth < bits_per_second) bandwidth = bits_per_second;
>      }
>      return (int64_t)bandwidth;
> --
> 2.1.0.rc2.206.gedb03e5
>

could anyone please look into this? thanks!