On 18 July 2016 at 01:34, Soft Works <softwo...@hotmail.com> wrote:
> This commit addresses the following scenario:
>
> we are using ffmpeg to transcode or remux mkv (or something else) to mkv.
> The result is being streamed on-the-fly to an HTML5 client (streaming
> starts while ffmpeg is still running). The problem here is that the client
> is unable to detect the duration because the duration is only written to
> the mkv at the end of the transcoding/remoxing process. In matroskaenc.c,
> the duration is only written during mkv_write_trailer but not during
> mkv_write_header.
>
> The approach:
>
> FFMPEG is currently putting quite some effort to estimate the durations of
> source streams, but in many cases the source stream durations are still
> left at 0 and these durations are nowhere mapped to or used for output
> streams. As much as I would have liked to deduct or estimate output
> durations based on input stream durations - I realized that this is a hard
> task (as Nicolas already mentioned in a previous conversation). It would
> involve changes to the duration calculation/estimation/deduction for input
> streams and propagating these durations to output streams or the output
> context in a correct way.
> So I looked for a simple and small solution with better chances to get
> accepted. In webmdashenc.c I found that a duration is written during
> write_header and this duration is taken from the streams' metadata, so I
> decided for a similar approach.
>
> And here's what it does:
>
> At first it is checking the duration of the AVFormatContext. In typical
> cases this value is not set, but: It is set in cases where the user has
> specified a recording_time or an end_time via the -t or -to parameters.
> Then it is looking for a DURATION metadata field in the metadata of the
> output context (AVFormatContext::metadata). This would only exist in case
> the user has explicitly specified a metadata DURATION value from the
> command line.
> Then it is iterating all streams looking for a "DURATION" metadata (this
> works unless the option "-map_metadata -1" has been specified) and
> determines the maximum value.
> The precendence is as follows: 1. Use duration of AVFormatContext - 2. Use
> explicitly specified metadata duration value - 3. Use maximum (mapped)
> metadata duration over all streams.
>
> To test this:
>
> 1. With explicit recording time:
> ffmpeg -i file:"src.mkv" -loglevel debug -t 01:38:36.000 -y "dest.mkv"
>
> 2. Take duration from metadata specified via command line parameters:
> ffmpeg -i file:"src.mkv" -loglevel debug -map_metadata -1 -metadata
> Duration="01:14:33.00" -y "dest.mkv"
>
> 3. Take duration from mapped input metadata:
> ffmpeg -i file:"src.mkv" -loglevel debug -y "dest.mkv"
>
> Regression risk:
>
> Very low IMO because it only affects the header while ffmpeg is still
> running. When ffmpeg completes the process, the duration is rewritten to
> the header with the usual value (same like without this commit).
>
> Signed-off-by: SoftWorkz <softwo...@hotmail.com>
> ---
> libavformat/matroskaenc.c | 39 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
> index 53353bd..75ee9fb 100644
> --- a/libavformat/matroskaenc.c
> +++ b/libavformat/matroskaenc.c
> @@ -44,6 +44,7 @@
> #include "libavutil/mastering_display_metadata.h"
> #include "libavutil/mathematics.h"
> #include "libavutil/opt.h"
> +#include "libavutil/parseutils.h"
> #include "libavutil/random_seed.h"
> #include "libavutil/rational.h"
> #include "libavutil/samplefmt.h"
> @@ -1487,6 +1488,30 @@ static int mkv_write_attachments(AVFormatContext *s)
> return 0;
> }
>
> +static int64_t get_metadata_duration(AVFormatContext *s)
> +{
> + int i = 0;
> + int64_t max = 0;
> + int64_t us;
> +
> + AVDictionaryEntry *explicitDuration = av_dict_get(s->metadata,
> "DURATION", NULL, 0);
> + if (explicitDuration && (av_parse_time(&us, explicitDuration->value,
> 1) == 0) && us > 0) {
> + av_log(s, AV_LOG_DEBUG, "get_metadata_duration found duration in
> context metadata: %" PRId64 "\n", us);
> + return us;
> + }
> +
> + for (i = 0; i < s->nb_streams; i++) {
> + int64_t us;
> + AVDictionaryEntry *duration =
> av_dict_get(s->streams[i]->metadata, "DURATION", NULL, 0);
> +
> + if (duration && (av_parse_time(&us, duration->value, 1) == 0))
> + max = FFMAX(max, us);
> + }
> +
> + av_log(s, AV_LOG_DEBUG, "get_metadata_duration returned: %" PRId64
> "\n", max);
> + return max;
> +}
> +
> static int mkv_write_header(AVFormatContext *s)
> {
> MatroskaMuxContext *mkv = s->priv_data;
> @@ -1495,6 +1520,7 @@ static int mkv_write_header(AVFormatContext *s)
> AVDictionaryEntry *tag;
> int ret, i, version = 2;
> int64_t creation_time;
> + int64_t metadataDuration;
We don't use CamelCase for anything but structs. Don't you see the variable
above and basically everywhere?
Change it to metadata_duration.
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